The blockade of the town was now made so sure, that Alkibiadês departed with a portion of the army to levy money and get together forces for the siege of Byzantium afterwards. During his absence, Theramenês and Thrasybulus came to terms with Pharnabazus for the capitulation of Chalkêdon. It was agreed that the town should again become a tributary dependency of Athens, on the same rate of tribute as before the revolt, and that the arrears during the subsequent period should be paid up. Moreover, Pharnabazus himself engaged to pay to the Athenians twenty talents on behalf of the town, and also to escort some Athenian envoys up to Susa, enabling them to submit propositions for accommodation to the Great King. Until those envoys should return, the Athenians covenanted to abstain from hostilities against the satrapy of Pharnabazus.[192] Oaths to this effect were mutually exchanged, after the return of Alkibiadês from his expedition. For Pharnabazus positively refused to complete the ratification with the other generals, until Alkibiadês should be there to ratify in person also; a proof at once of the great individual importance of the latter, and of his known facility in finding excuses to evade an agreement. Two envoys were accordingly sent by Pharnabazus to Chrysopolis, to receive the oaths of Alkibiadês, while two relatives of Alkibiadês came to Chalkêdon as witnesses to those of Pharnabazus. Over and above the common oath shared with his colleagues, Alkibiadês took a special covenant of personal friendship and hospitality with the satrap, and received from him the like.
Alkibiadês had employed his period of absence in capturing Selymbria, from whence he obtained a sum of money, and in getting together a large body of Thracians, with whom he marched by land to Byzantium. That place was now besieged, immediately after the capitulation of Chalkêdon, by the united force of the Athenians. A wall of circumvallation was drawn around it, and various attacks were made by missiles and battering engines. These, however, the Lacedæmonian garrison, under the harmost Klearchus, aided by some Megarians under Helixus, and Bœotians under Kœratadas, was perfectly competent to repel. But the ravages of famine were not so easily dealt with. After the blockade had lasted some time, provisions began to fail; so that Klearchus, strict and harsh, even under ordinary circumstances, became inexorable and oppressive, from exclusive anxiety for the subsistence of his soldiers; and even locked up the stock of food while the population of the town were dying of hunger around him. Seeing that his only hope was from external relief, he sallied forth from the city to entreat aid from Pharnabazus; and to get together, if possible, a fleet for some aggressive operation that might divert the attention of the besiegers. He left the defence to Kœratadas and Helixus, in full confidence that the Byzantines were too much compromised by their revolt from Athens to venture to desert Sparta, whatever might be their suffering. But the favorable terms recently granted to Chalkêdon, coupled with the severe and increasing famine, induced Kydon and a Byzantine party to open the gates by night, and admit Alkibiadês with the Athenians into the wide interior square called the Thrakion. Helixus and Kœratadas, apprized of this attack only when the enemy had actually got possession of the town on all sides, vainly attempted resistance, and were compelled to surrender at discretion: they were sent as prisoners to Athens, where Kœratadas contrived to escape during the confusion of the landing at Peiræus. Favorable terms were granted to the town, which was replaced in its position of a dependent ally of Athens, and probably had to pay up its arrears of tribute in the same manner as Chalkêdon.[193]
So slow was the process of siege in ancient times, that the reduction of Chalkêdon and Byzantium occupied nearly the whole year; the latter place surrendering about the beginning of winter.[194] Both of them, however, were acquisitions of capital importance to Athens, making her again undisputed mistress of the Bosphorus, and insuring to her two valuable tributary allies. Nor was this all the improvement which the summer had operated in her position. The accommodation just concluded with Pharnabazus was also a step of great value, and still greater promise. It was plain that the satrap had grown weary of bearing all the brunt of the war for the benefit of the Peloponnesians, and that he was well disposed to assist the Athenians in coming to terms with the Great King. The mere withdrawal of his hearty support from Sparta, even if nothing else followed from it, was of immense moment to Athens; and thus much was really achieved. The envoys, five Athenians and two Argeians,—all, probably, sent for from Athens, which accounts for some delay,—were directed, after the siege of Chalkêdon, to meet Pharnabazus at Kyzikus. Some Lacedæmonian envoys, and even the Syracusan Hermokratês, who had been condemned and banished by sentence at home, took advantage of the same escort, and all proceeded on their journey upward to Susa. Their progress was arrested, during the extreme severity of the winter, at Gordium in Phrygia; and it was while pursuing their track into the interior at the opening of spring, that they met the young prince Cyrus, son of king Darius, coming down in person to govern an important part of Asia Minor. Some Lacedæmonian envoys, Bœotius and others, were travelling down along with him, after having fulfilled their mission at the Persian court.[195]