The tenth-century Armenian architect Trdat is known to historians of both Byzantine and Armenian architecture because of the bicultural nature of his works: he is credited with the repair of the dome of the Hagia Sophia in Constantinople and with the construction of Ani Cathedral in Armenia, one of the best-known medieval monuments of the Caucasus. In a comparative exploration of Trdat's Byzantine and Armenian work, and a textual study of a little-known Armenian source, the essay offers not only insight into cross-cultural exchange in Byzantium and Armenia, but also new information on building practices in the Christian East.