The study surveys a major Byzantine church in Constantinople, reconstructing its site and historical phases, compiling contemporary descriptions and a descriptive poem, and furnishing extensive measured drawings and illustrations. It analyzes architectural form and construction—plans, domes, arches, vaulting, mortar, marble cladding, capitals, doors, mosaics, and glass—alongside liturgical fittings, relics, and ceremonial use. Later repairs, restorations, precincts, and vernacular building practices are examined to argue that practical craft, materials, and local tradition shaped Byzantine design. Field observation, translations of primary sources, and material analysis support the book’s technical and historical conclusions.