One of the most significant monuments in Istanbul's history has been one of its least fortunate survivors. A large rotunda from an Late Roman palace was incorporated as the substructure for the palace of Romanos Lecapenos in the early tenth century. The church, adjacent to Romanos' palace, was built on separate substructures, into which a funerary chapel was added in the Late Byzantine period. The site thus represents three major periods in the Byzantine history of the city.
The church, now Bodrum Camii, suffered in a disasterous restoration in 1964-65 that replaced 90% of the exterior masonry with concrete bricks, altering the lines of the building. This restoration was abandoned before completion, and the building was re-restored in the late 1980s to a more satisfying appearance, although there is virtually no original surface left on the building.
The rotunda had been converted to a cistern when the tenth-century palace was added, with the insertion of dozens of columns to support the vaulting. In the early 1990s bulldozing for the construction of a hotel next door damaged the cistern. In 1993-94, the cistern was cleared, cleaned, and replastered by developers, who have turned it into a shopping bazaar -- one of the most surprising adaptive reuse projects I've seen. The terrace above was paved with marble. A photo by Tunay shows the extrados of the cistern vaults during this work.