In this Lecture I have to deal with the products of a school of architecture, Celtic in its character, and absolutely peculiar to the Scottish area.

On the small uninhabited island of Mousa, lying off the east coast of the mainland of Shetland, there stands a solitary stone structure, massive in size, peculiar in appearance, and still more peculiar in character. It is a tower of circular form, wide and lofty, but constructed of undressed stones laid upon each other without mortar or other binding material, so that the mass of its uncemented wall coheres simply by its own vertical pressure.

Its situation is peculiar. The island is small, not over a mile in length, and less than half a mile in width, bare, flat, and rocky. The tower is placed on a small promontory on the west side of the island at the point nearest to the mainland. It stands about 20 feet back from the edge of the rocks, which slope irregularly to the tide-mark about 20 feet below. There are slight remains of an intrenchment on the sides which look landward, those facing the rocks and the sea are protected by the natural features of the ground.

The material of which the tower is built is the fissile flag of the island. The stones are flat, sometimes as much as 2 feet in thickness, but mostly much less, and they rather diminish in size towards the top of the tower. The stones bear no mark of a tool, and the masonry is not coursed, but compactly fitted together. The wall goes up with a curve like that of a lighthouse, and its external appearance (Fig. 160) is suggestive of great solidity and strength. This suggestion of solidity, which is due to the bulk of the building rather than to the character of its masonry, is further intensified by the absence of external openings, the whole exterior surface being unbroken by a single aperture except the doorway. It is on the level of the ground on the S.W. side, and is about 5 feet 3 inches high by 2 feet 11 inches wide, passing straight through the thickness of the wall, but widening considerably at a distance of about 7 feet from the outside and rising in the roof. Entering by this tunnel-like passage through a wall 15 feet 6 inches thick, the visitor finds himself in the interior of a circular well-like court, open to the sky above, but completely surrounded by a wall of that thickness and 45 feet in height. From the inner circumference of this court (as seen in the ground plan, Fig. 161) there open at various places other doorways leading into oval chambers constructed in the thickness of the wall nearly on the ground level. These chambers are three in number. One placed to right of the entrance is 16 feet in length, 5 feet 9 inches wide, and 9 feet 9 inches high. Its doorway is small, 3 feet high and 2 feet wide, passing through 4 feet of the thickness of the wall. A second chamber opposite the main entrance is 14 feet long, 6 feet 10 inches wide, and 10 feet 6 inches high. Its doorway is also small, 3 feet 4 inches high and 2 feet 9 inches wide, passing through a thickness of 4½ feet of walling. The third chamber, situated to the left of the main entrance, is 14 feet long, 5 feet 6 inches wide, and 9 feet 6 inches high. Its doorway is 3 feet 2 inches high and 2 feet 3 inches wide, passing through 4 feet of walling. All these chambers are irregularly oval in form on the ground plan. They are roofed in a peculiar manner. At variable distances from the floor the walls begin to be brought inwards by projecting each stone slightly beyond the face of the stone below it. In this way the distance between the opposite walls is gradually lessened as they rise in height until they come near enough to admit of single stones being laid across the space between wall and wall. This style of converging the walls inwards to obtain support for a roof of single stones is not new to us. We have met with it in the beehive houses of the early Christian monasteries and in the inverted boat-shaped roofs of their churches, built of uncemented stones on a rectangular ground-plan. It is the style of roof which is common to all dry-built structures that are roofed, whether they be of Pagan or of Christian time, because it is the style that is best suited to the material and the manner of construction. The builders of this edifice had no stones long enough to span chambers of six feet wide, and if they had had them long enough they would have been too weak to bear the superincumbent weight of a wall forty feet in height. Therefore they made their chamber-roofs semi-vaulted, while the doors and passages, which were narrow, were simply spanned with strong flat lintels. These chambers on the ground floor are lighted by window-like openings above the doorways, which rise one over the other, and serve not only to admit light and air, but to distribute the weight to be borne by the lintels. In each of the chambers there are small ambry-like recesses in the walls, but no fireplace or chimney. They are small, dimly-lighted, dungeon-like rooms, but neither smaller, worse-lighted, or more dungeon-like than many rooms in the lime-built castles of the nobles of the Feudal ages.

Half-way between the chamber facing the main entrance and the one to the left of it there is a doorway placed at a height of four feet above the ground level. This doorway, which is higher and wider than those which lead into the chambers, is slightly larger than the main entrance itself, being 5 feet 4 inches high and 3 feet wide. It leads to a stair constructed like the chambers within the thickness of the wall. At the foot of the stair there is an oval chamber, from one end of which the stair rises in a steep slope, but following the curve of the wall to the top. The steps are single flat stones, varying in width from ten inches to two feet, undressed, and laid above each other so that they give a tread of about five inches and nearly the same of a rise. The upper part of the tower which is traversed by the stair is differently constructed from the lower part. To the height of about eleven feet above the ground level the wall of the tower is carried up solid except for the vacancy occasioned at intervals in its thickness by the chambers and their accesses. But above this height the wall is carried up with a vacancy in its centre (as seen in the section Fig. 162) so as to form a series of circular galleries placed one immediately over another, and crossed successively from the lowest to the highest by the rise of the stair which gives access to them.

These galleries, situated in the heart of the wall, are six in number. Each begins about 3 feet 9 inches in front of the stair, and goes round the whole tower on the level till it comes against the back of the stair, which closes it at that end, so that entrance to the gallery or exit from it can only be obtained by stepping across the space intervening between the end of the gallery floor and the steps of the stair. The floors of the galleries are formed of flat undressed slabs, the end of which reach into the walls on both sides. These slabs are about 6 inches thick, and those whose under surfaces form the roof of the first gallery present their upper surfaces as the floor of the second, and so throughout. None of the galleries exceed 5 feet 6 inches in height or 3 feet 2 inches in width, and some of the upper spaces are now much narrower; but as the position of the upper walls has evidently shifted, the original dimensions of the upper galleries cannot be ascertained. Four of the galleries that now remain (for the tower is incomplete at top) are lighted by four vertical ranges of windows all looking into the interior court. One range of fourteen openings is over the main entrance. Another of eighteen openings is over the entrance to the stairs. The third set has seventeen openings, and the fourth is imperfect, many of the lintels having been broken out. The peculiarities of these windows are—(1) that they are placed close to each other, vertically, with merely the thickness of a lintel between each opening; (2) they are wider than they are high, the greatest width being 2 feet 9 inches, and the greatest height not exceeding a foot; (3) they diminish in size gradually from the lowest to the highest; and (4) they do not range so far upwards as to include the two upper galleries, which are windowless.

Let us now group the main features of this singular building. It is a circular tower, composed of a dry-built wall 15 feet thick, enclosing a court 20 feet in diameter. The wall rises to a height of 45 feet, and has no opening to the outside except the doorway which gives access to the court. Opening from the court are a series of chambers on the ground floor constructed in the thickness of the wall and rudely vaulted with overlapping masonry. Above these are successive ranges of level galleries, also in the thickness of the wall, each going round the tower, and placed so that the roof of the one below always forms the floor of the next above. These galleries are crossed successively by a stair from which access to them is obtained by facing round in the ascent and stepping across the vacant space forming the well of the stair. The three lower galleries only are lighted, and the windows are placed in vertical ranges so close to each other as to be separated only by their upper and lower lintels.

Each of these features, taken by itself, is specially remarkable, and the presence in the one building of such a group of features that are wholly unfamiliar to us invests it with a character that is distinctly peculiar. From this examination of its character, it becomes obvious that although the construction and arrangements of the building are clearly those of a place of strength, it is incapable of association by way of relationship with any variety of castle known in historic times. But a wider survey of the remains of the ancient strongholds of the people who have occupied the land in times of which we have no distinct or detailed historic record will show that it has relationships so close as to amount to an almost actual identity with many similar structures in different parts of Scotland.

For instance, in the small valley of Glenbeg, which runs nearly parallel with Glenelg, in the west of Inverness-shire, there are two such structures. One is situated on the edge of the meadow which lies in the bottom of the valley. It is greatly destroyed; more than half the circle of the wall is gone, and part of the height of the portion that remains is wanting. The internal diameter of the tower, at the level of the rubbish which encumbers the floor, is 33½ feet, and the thickness of the wall 11 feet. The doorway (Fig. 163), which is the only opening to the outside, is 3 feet 5 inches wide at the head, the lower part concealed with rubbish. About 4 feet inside the outer plane of the wall there is a rebate for a door (Fig. 164), with checks in the shape of large slabs set edgewise in the wall. Within these checks the passage widens to 5 feet, and the roof rises as shown in the section, Fig. 165. On the south side of the passage there is a guard-chamber opening from it, and constructed in the thickness of the wall. Three galleries and part of a fourth remain, but the stair is gone. The galleries are lighted by vertical ranges of windows looking to the interior. The greatest height of wall remaining is not over 30 feet, but 7 feet of its height were taken by the contractor for the Bernera Barracks in 1722. It must therefore, before that time, have been nearly as high as Mousa now is.

At the distance of less than a mile up the valley on the same side, and placed on a considerable eminence, is another ruined structure of the same kind (Fig. 166), but more dilapidated. No part of the height now exceeds 25 feet. The diameter of the tower internally has been about 30 feet, and the wall is 12 feet thick. Traces of chambers on the ground floor are visible, but choked with rubbish. The door and stairs are gone. Three galleries remain in part. The first is 6 feet high and 4 feet wide, the second 6 feet high and 3½ feet wide, the third inaccessible and somewhat smaller.

These structures, so far as their distinctive features remain unobliterated, present a striking similarity alike in the manner of their construction and the nature of their arrangements to those of Mousa. They vary in certain details, as in size, in thickness of wall, in the presence of a guard-chamber in connection with the passage, but in all the essential features of plan, construction, and arrangements they are substantially the same.

Near the head of Loch Duich, a few miles from Glenelg, is another ruined tower. It stands on the slope of an eminence close under a high crag. The lower part of the structure is entire, but little remains of its height. Its internal diameter is 31 feet, its thickness of wall 12 feet. The doorway is in the lower side of the building facing the N.E. It is 3 feet wide at the outside, and at 4 feet 3 inches within the outer plane of the wall (Fig. 167) there is a rebate for a door with checks formed of long slabs 9 inches thick, set edgewise in the wall. Behind these is a bar-hole on either side for a long stout bar. The hole, on one side, is long enough for the bar to lie in it permanently, and on the other only long enough to receive its end when pulled across behind a door either constructed of wood or formed of a slab of stone set up against the checks. On the S.E. side of the entrance passage (Fig. 168) is a doorway 18 inches wide and 3 feet high, giving Fig. 168.—Sectional elevation of S.E. side of entrance passage of the Broch at Loch Duich, showing doorway of guard-chamber, and bar-hole (wall 12 feet thick).
Fig. 168.—Sectional elevation of S.E. side of entrance passage of the Broch at Loch Duich, showing doorway of guard-chamber, and bar-hole (wall 12 feet thick). access to an oval guard-chamber constructed in the thickness of the wall, 12 feet long, 6 feet wide, and about 7 feet high, roofed in the usual manner by overlapping masonry and flat stones laid across. There are traces of other chambers on the ground floor, and part of a gallery remains over the entrance, but all above is gone. The masonry of this tower is more massive than that of those in Glenbeg, but the general plan and manner of construction are precisely similar in character. In point of fact there is so little deviation from the typical plan of construction among all the examples that are known, that the detailed descriptions of them are for the most part repetitions of features that are closely similar. But as we are dealing with buildings that are in ruins, and, as it appears, with a class of buildings of which no complete example is now known to exist, it is important to determine if possible whether there may be sufficient ground for assigning to the class the general feature of height, of which, in the majority of cases, no direct evidence now remains.

There is distinct evidence on record that a number of these massively built towers were of considerable height. George Low, in 1774, says of the ruined tower or Broch of Burraness, in the island of Yell, in Shetland, that it had an inside diameter of 31 feet, a thickness of wall of 10 feet, and a total height of 20 feet. Of the Cullswick Broch he says that its internal diameter was 26 feet 6 inches, its thickness of wall 18 feet, and the total height remaining 23 feet. Castle Cole (Fig. 169), at the junction of the Blackwater and the Brora, was then 15 feet in height, and part of it still remains of about that height. Dun Dornadilla, in Sutherlandshire (Fig. 170), as described by Mr. Cordiner in 1776, and Mr. Pope of Reay, in 1777, had an internal diameter of 27 feet, and the total height then remaining was estimated at 25 to 30 feet, with three galleries and part of the stair. Maitland, in 1757, describes Dun Alisaig, in Ross, as being 30 feet internal diameter, with 12 feet thickness of wall, and three of the galleries remaining, which implies a height of 25 to 30 feet. Dun Carloway, in Lewis, was 40 feet high in the end of last century, and showed the plan of its galleries with their vertical ranges of windows almost as completely as Mousa. Judging from these examples, which still have, or which in recent times have had a considerable portion of their height remaining, and taking into account the quantity of material which envelops the bases of most of those that have been reduced to the condition of mere mounds of ruin, it seems established by evidence that there were many cases in which the total original height could scarcely have been less than that of Mousa, and that height, as well as bulk, was one of the main features of the typical structure.

These examples will suffice to convey a clear idea of the distinctive features of the type of structure with which we are dealing. Its main features of distinction, by which it separates itself from all known types, are (1) that it is a circular tower of dry-built masonry, wide and lofty, and enclosing within it a central area open to the sky; (2) that all its apertures, except the external opening of the entrance to the central area, look into this enclosed interior court; and (3) that its chambers, stair, and galleries are contained within the thickness of this enclosing wall.

Having thus obtained a distinct conception of the type, we now proceed to determine its range or area. For this purpose it is necessary to ascertain what structures exist in Scotland, or out of it, possessing these typical features.

On the northern declivity of Cockburn Law, in Berwickshire, there is a natural platform projecting from the shoulder of the hill over the valley of the Whitadder water, about 250 feet above the bed of the stream. On this platform there is an irregularly oval enclosure (Fig. 171), the outlines of which are formed by the remains of two parallel earthworks and an outside ditch. The space thus enclosed is occupied by the remains of various smaller enclosures, some circular and others irregular in form. They are nearly all so ruined that nothing can be made of their details. But the principal structure within the enclosure is still capable of such examination as will suffice to determine its typical relationship with the Brochs of the extreme north. It is circular, consisting of a wall 17 feet thick, enclosing an area of 56 feet in diameter. In the thickness of this wall are two elongated oval-shaped chambers, one of which is 33 feet long and 7 feet wide, the other 23 feet long and 7 feet wide. In 1793 the roofs were still on them, and it was then seen that they were covered with a rude vaulting of overlapping masonry. Both these chambers open to the inner area. The only access to this area from the outside is the main doorway, which passes straight through the wall, and is flanked by a guard-chamber constructed in the thickness of the wall on either side. To the left of the doorway are the remains of the staircase, with an elongated chamber opposite the foot of the stair. No remains of galleries exist owing to the absence of the whole upper part of the structure, but the presence of the stair implies that they once existed. The masonry is massive in character (Fig. 172), and the structure is also remarkable for its great size, being three times the width of Mousa and twice that of the Glenelg Brochs. But its features of form and character, and all the arrangements of its details, so far as they now exist, are those of the typical Broch structure; and, taken together, they form a group of features and arrangements which do not exist in any other type of structure.

On the highest elevation of the Torwood, in the parish of Dunipace in Stirlingshire, are the remains of a circular structure, excavated in 1864 by Colonel Joseph Dundas. Its appearance previous to its excavation was that of a conical hillock situated nearly on the verge of a precipitous crag, and enclosed on the accessible side by the remains of a double wall of fortification. After excavation it was found to be the ruin of a circular tower of uncemented masonry which, by the gradual dilapidation of its walls, had become a conical hillock of stones covered with grass and heather, and overgrown by a clump of large fir-trees. The structure, now cleared from the superincumbent mass of ruin, is a circular wall 15 feet thick, enclosing a central area of 35 feet in diameter. The entrance doorway has some of the massive lintels still upon it. It is about 7 feet high and 3 feet wide at the door-checks, behind which are the usual bar-holes (shown at A A in the ground plan and section, Figs. 173, 174). To the left of the doorway is the staircase, as usual in the thickness of the wall. The height of wall remaining is not sufficient to show any traces of the galleries, but the presence of the stair implies their former existence. There are no chambers in the thickness of the wall on the ground floor, but all the other features of the building are those of the typical Broch structure.

On the other side of the valley of the Forth, and farther west, at Coldoch, in Perthshire, a similar mound, covering the ruins of a circular tower of uncemented masonry, was excavated in 1870. The structure consists of a circular wall (as shown on the ground plan, Fig. 175) 17 feet thick, enclosing a central area of 30 feet in diameter. The doorway on the east side passes straight through the wall, and is three feet wide, with checks for the door about half-way through the thickness of the wall, and immediately behind them the usual bar-holes. To the left of the doorway is the staircase. No remains of the upper galleries exist, but the presence of the stair implies that they did exist. Opening from the central area are the entrances to three chambers in the thickness of the wall. They are nearly of a size, 8 feet long, 4 feet wide, and a little over 6 feet high. One still retains its roof, rudely vaulted with overlapping masonry. In this case also the group of features characteristic of the structure and its arrangements is such as can be found only in the typical structure of the Broch.

These three examples are all that are known on the mainland of Scotland south of the Caledonian valley. A few years ago they were mere grass-covered hillocks, indistinguishable from many others that are yet to be seen in various quarters of the same wide district of country. It is impossible to say how many of these unexamined mounds, which exist abundantly in the valleys of the Forth and Teith for instance, may be of similar character. But it is possible to say that where three have been found without being specially looked for, the probability is that more will be found when they are looked for. The present position of our knowledge is that there are three examples south of the Caledonian valley, but if I were to conclude that these three are all that exist in that wide region I should be drawing from my ignorance of the actual facts a conclusion which could only be drawn from complete knowledge obtained by exhaustive investigation.

The case is far otherwise with reference to the district of country that lies to the north of the Caledonian valley and the isles around the northern and western coasts. In such remote and frequently rugged and barren localities the remorseless activity of the agricultural improver has made but little progress in the removal of the ancient landmarks, and Brochs, and sepulchral cairns, stone circles and standing monoliths are still comparatively abundant, though every season diminishes their number. Some years ago I attempted an enumeration of the remains in the northern counties of Scotland that were either certainly known to be Brochs or were inferred to possess that character, judging from external appearances. The list has been published^[72] for seven years, and the corrections made upon it during that time have not appreciably affected its total results. These are roughly stated as follows:—in Shetland, there are 75 Brochs; in Orkney, 70; in Caithness, 79; in Sutherland, 60; in Ross-shire, 38; and in Inverness-shire, 47; giving a gross total for the five northern counties of Scotland of 370. Admitting that there must be some instances included in the enumeration which subsequent examination may prove to be remains of a different character, it is equally probable that others will be found which have not been included in the list, and the errors in these opposite directions may be expected nearly to balance each other. But if we suppose that it will be necessary to deduct so large a proportion as 20 per cent, we should still have a gross total of 300 Brochs in the five northern counties. The full significance of such a result is scarcely realised at once. It means that we have here the remains of a period of architectural activity which has no parallel in the early history of our country.

Whatever may be the effect of future discoveries in increasing the number of examples in the district south of the Caledonian valley, it is clear that the principal area of the type lies within the region to the north of that valley, comprehending the five northern counties of Scotland, and including the northern and western Isles. Within that area they are known to exist abundantly, beyond it sparsely. Out of Scotland the type is totally unknown. It is a type possessing features so distinct and peculiar, so numerous and well marked, so pronounced in their absolute individuality, that if it exists anywhere it is capable of being instantly recognised. But no single instance occurs in Ireland, or Wales, or Cornwall. No trace of it is found in England, France, or Scandinavia. It is absolutely confined to Scotland alone.^[73] Having thus established the essential features of the typical form of the Broch structure and determined the area to which it is exclusively confined, I now proceed to notice a few other examples possessing features which may not have been present or prominent in those previously described.

We have already seen that many of these towers were built in positions that were naturally strong. One of the most remarkable of these is the Broch of Cole’s Castle in Strathbrora, Sutherlandshire (Fig. 178), which has been already referred to. It is situated on the top of an isolated eminence, precipitous on one side, and defended on the side which is less precipitous by a double fortification of dry-stone walling. Others whose situations made them capable of being so defended were protected by ditches and embankments. The Broch of Snaburgh, in the island of Unst, in Shetland, which stands on a promontory projecting into the loch, is protected on the land side by a wet ditch and a rampart of large stones. The Broch of Burraness, in the same island, is strengthened on the land side by two deep ditches and high embankments. The Broch of Cullswick was protected by a ditch 13 feet wide, and a rampart of earth and stones completely encircling the base of the tower. The Broch of Burraland, which stood on a promontory in the loch, had a double rampart and a double wet ditch on the land side, both well defined. The Broch of Yarhouse, in Caithness, stood on a low flat promontory projecting into the loch, and was cut off from the land by a deep ditch from 25 to 30 feet wide, and had its doorway further protected by a long covered way. The Broch of Clickamin, at Lerwick (Fig. 179), although situated on an island in the loch, was fortified by a wall completely surrounding the island. Within this outer wall of defence there is an outwork or guard-house, in form a segment of a circle, 43 feet on its convex face, connected with the outer wall by a passage. The outwork is 19 feet wide at the passage through it, slightly narrower at the ends. The passage is 8 feet high, and about 5 feet in from the outer face of the work it narrows to 2 feet 11 inches, with checks for a door. Behind these are holes in the opposite walls for a bar and a slit in the roof of the passage. Besides these two exterior defences the doorway of the tower itself had checks and a sill for a door about 10 feet within the outer opening of the entrance passage through the wall of the Broch. This passage is 4 feet 10 inches high, and the opening between the door-checks is 2 feet 11 inches wide at the bottom and 2 feet 6 inches at the top, with bar-holes on either side.

The East Broch of Burray, in Orkney, explored by Mr. Farrer, presented the appearance of a green mound 20 feet high, surrounded by an embankment. The mound when excavated was found to cover the lower portion of a circular tower of uncemented masonry (Fig. 180). The wall of the tower was 15 feet thick, enclosing a central area 36 feet in diameter. The entrance passage as usual went straight through the wall, and had a guard-chamber opening from it on either side. The entrance to one of these is shown in the section and the bar-hole behind it. There were two other chambers constructed in the thickness of the wall opening from the central area, and the entrance to the stair was placed as usual to the left of the doorway, but on a higher level. In all its features it closely resembles all that have been described, but in one feature it differs from them. Close to the doorway, but outside the wall, there is a well with a passage and steps leading down into it. There are other examples which exhibit the same feature.

The Broch of Borrowston, in Shapinsay (Fig. 181), also in Orkney, consisted of a wall 13 feet thick, enclosing a central area 33 feet in diameter. Within the central area of the Broch there was a well 10 feet deep, the lower part dug out of the solid rock, and the upper part faced with dry-built masonry. The Broch of Okstrow, at Birsay in Orkney, which consisted of a wall 12 feet thick, enclosing an area 45 feet in diameter, had a well within the area and a drain from it leading out to the outside of the structure. The Broch near the Manse at Harray (Fig. 182), excavated by Rev. Dr Traill, consisted of a wall 12 feet thick, enclosing an area about 33 feet in diameter. It was surrounded by outbuildings, which were not properly explored. There were no guard-chambers on either side of the passage (B), which shows the checks for the door, at 6 feet within the outer face of the wall. To the left of the main entrance is the usual chamber (H) at the foot of the stair (G), of which 19 steps remain; and two other oval chambers (E and F), placed at nearly equal distances in the circumference of the wall, complete the resemblance to the general type. Near the middle of the area a subterranean passage terminating in five steps led to a well (D) 9 feet deep excavated in the rock. The subjoined sectional diagram (Fig. 183) shows the construction of the well, which still retained water when the excavation of the Broch was made. The Brochs of Skinnet, Harpsdale, and Kettleburn in Caithness, had each a well within the central area. The well of the last-mentioned Broch is still utilised as the existing water supply for the cottars, who live in houses close by constructed of the stones removed from the site of the ancient structure.

The central areas of several Brochs have been provided with drains to convey the surface water outside the building. This same Broch of Kettleburn had a drain which passed out under the foundation of the wall of the tower. It was what is now called a self-cleansing drain, the flat stones forming the water channel being set together in the form of the letter V. Sir Henry Dryden remarks the presence of drains in the Broch of Clickamin. I found a square drain leading from the court of a Broch which I excavated at Brounaben, in the parish of Wick.

The facts that many of these structures were thus provided with drainage, and that they had also secured a water-supply within the enclosed area of the building, are not only significant indications of intelligence and forethought applied to the arrangement of constructional details, but when taken in connection with all the other arrangements of the structure external and internal, they complete a series of characteristics which point definitely to one object as the chief intention of the Broch-structure, viz. security obtained by the simplest of all means—a construction of uncemented stones which could neither be easily forced nor readily reduced.^[74]

Reviewing the typical characteristics of the special form of structure which has come to be known in recent years by the local northern name Broch, we see that it is a hollow circular tower of dry-built masonry, rarely more than 70 or less than 40 feet in its total diameter, and occasionally at least 50 feet high. Its circular wall, which may be from 9 to 20 feet thick, is carried up solid for about 10 feet, except where it is pierced by the entrance, or partially hollowed by the construction within its thickness of oblong chambers with rudely-vaulted roofs. Above this height the wall is carried up with a vacancy of about 3 feet wide between its exterior and interior portions. At every 5 or 6 feet of its height this vacancy is crossed by horizontal ranges of slabs inserted as ties between the outer and inner shells of the wall, so that their upper surfaces form a floor to the space above and their under surfaces become a roof to the space below. These spaces thus form horizontal galleries about 6 feet high and 3 feet wide, separated from each other vertically by the slabs of their floors and roofs. They run completely round the tower except that they are crossed successively by the stair which gives access to them. They are lighted by ranges of peculiarly-constructed windows placed vertically over each other, and all looking into the central area enclosed by the wall of the tower. This area or court varies from 20 to 45 feet in diameter. At various points of its interior circumference are placed the openings which give access to the chambers on the ground floor within the wall, and to the stair which ascends to the galleries. The only aperture on the outside of the tower is the doorway formed by the external opening of the tunnel-like passage through the wall which gives access to the central court. It is always on the ground level, square-headed, usually with slightly inclined sides,^[75] 5 to 6 feet high, and rarely more than 3 feet wide, passing straight through the thickness of the wall, and thus varying from 9 to 18 feet in length. Some 4 feet or thereby within the outer end of the passage there is a rebate of the masonry faced with strong slabs inserted edgewise in the wall, and forming checks for a door, behind which are the bar-holes, and behind them the opening of a guard-chamber built in the thickness of the wall.

On further consideration of this remarkable group of excessively peculiar features, it becomes evident that they all point more or less obviously to the presence of a double intention in the minds of the constructors of the Brochs. The design of the whole structure and the arrangements of all its separate parts exhibit a careful and laborious adaptation of means and material to the two main objects of shelter and defence. The clever constructive idea of turning the house outside in as it were, placing its rooms within its walls, and turning all their windows towards the interior of the edifice, implies boldness of conception and fertility of resource. The height of the wall, which effectually secured the inmates against projectiles, also removed its essentially weak upper part beyond reach of assault, while the pressure of its mass knit the masonry of the lower part firmly together, and its thickness made it difficult to force an entrance by digging through it—if such a wall could be approached for this purpose when the whole of its upper materials were deadly missiles ready to the hands of the defenders. The door, securely fastened by its great bar, is too strong to be carried by a rush. Placed four feet or more within the passage, it can only be reached by one man at a time, and the narrowness of the passage prevents the use of long levers. In all probability the door itself is a slab of stone, and impervious to fire. But even if it is forced, and entrance gained to the interior court, the enemy finds himself as it were in the bottom of a well 30 to 40 feet in diameter with walls 50 feet high, pierced on all sides by vertical ranges of windows, or loopholes, commanding every foot of the space below, and rising to the number of twenty or more, immediately over the door which gives access to the galleries. In short, the concentration of effort towards the two main objects of space for shelter and complete security was never more strikingly exhibited, and no more admirable adaptation of materials so simple and common as undressed and uncemented stone for this double purpose has ever been discovered or suggested. Perhaps there is no characteristic of the typical structure more remarkable than the extreme constancy of its essential features. The uniformity of plan and construction is so unvarying among all the known examples that there exists no means of tracing the development of the form through a series of primitive or immature stages. In this respect there is a striking analogy between the Brochs and the Round Towers of Ireland. The Irish Towers also appear fully developed, and exhibit a general uniformity of plan and construction which is quite as remarkable in its manifestations among them as it is among the Brochs.^[76] Their origin is assignable to peculiar circumstances in the history of the ecclesiastical communities, and chiefly to their constant liability to sudden danger of plunder and murder by roving bands of marauding Norsemen. This specialty of purpose accounts for, and harmonises with, their specialty of form; and their remarkable uniformity of plan is the natural result of the special fitness of the typical form for its special intention—the provision of a secure refuge from dangers which, though of frequent occurrence, were of transient duration.

In Scotland the area which is chiefly occupied by the Brochs was peculiarly exposed to similar occurrences. Over the whole of the northern and western districts there ebbed and flowed continuously for centuries a species of irregular intermittent warfare, consisting chiefly of plundering forays by bands of foreign marauders. And as the special association of the Round Towers of Ireland with the ecclesiastical sites of the country supplies the clue to their special purpose, the Brochs of Scotland have also their special association from which their special purpose may also be fairly deduced. Although they are often placed in situations of natural strength, yet, as a rule, they mark the area of the best land in the districts in which they are situated. This is specially true of their local distribution in Caithness, while in Sutherland we see them thickly planted in the fertile straths, and following the courses of the rivers to distances of twenty-five or thirty miles inland. They are therefore the defensive strongholds of a population located upon the arable lands, and not in the mountain fastnesses of the country; and their peculiar nature as exceptionally secure places of refuge for non-combatants and cattle, and for storage of produce, explains the fitness of their association with the arable soil of the area in which they are most abundantly present. Against such oft-recurring but transient dangers to the cultivators and to the produce of their soil there could be no more effective system of defence provided than a multitude of safes, which should be burglar-proof, and big enough to contain the families, goods, and cattle of their proprietors.^[77]

If it be thus suggested by the relations of the Brochs to the arable lands of the districts in which they are situated, that they belonged to the possessors and cultivators of the soil, the affinities of the typical structure itself go far to show that in its character and origin it is distinctively Celtic. None of its essential features have been observed in any construction outside of the Celtic area. And within that area no building with a stair and an arrangement of galleries similar to that of a Broch has been met with out of Scotland. But the circular wall, with chambers in its thickness, which may be regarded as the germ from which the Broch structure has grown, is a characteristic feature of Celtic construction. We have met with it in the walls of the cashels surrounding the ecclesiastical settlements of Christian times. It is common in Irish Cloghauns and Scottish beehive houses, and is so persistently Celtic that it appears also in Wales and Cornwall. The ground plan of the most perfect of a group of beehive huts at Bodinar, in Cornwall (Fig. 184), exhibits an arrangement of oval chambers in the thickness of its wall precisely similar to the arrangement which prevails in the Brochs. The long narrow gallery (the essential feature of the earth-houses of Scotland, Ireland, and Cornwall) is also a form of construction which is specially characteristic of the Celtic area. The typical Broch structure thus presents a combination of features and forms of construction^[78] which are found existing separately in other constructions of Celtic character and origin, although the typical combination which distinguishes the Broch structure from all others is confined to Scotland alone.