Saint Sophia the greatest example of Byzantine architecture. Is at the same time of considerable importance where Turkish art and culture are concerned. To epitomize the dual characteristic of this building. Which carries the traces of both Byzantine and Turkish civilization;' will here describe briefly the Byzantine Horologium and the Turkish period clock room. It is known that Saint Sophia once possessed a Horologium. According to the Arab Harun ıbn Yahya who was brought as a slave to Istanbul during the reign of Basileios I (867-886) according to same sources, and during the brief reign of Alexandros (912-913) according to other sources and who is recorded as being permitted to move freely around the city-the Horologium was a large room containing a cloak. Byzantine sources record that when the emperors visited Saint Sophia, they always passed in front of the Horologium. Researchers have put forward several theories as to the whereabouts of this Horologium. J. Ebersolt (1879-1933) asserts that it was demolished when the southwest minaret was constructed. Whereas Ö.M. Schneider (1896-1952) contends that it was a rectangular building jutting out from the south-west corner of Saint Sophia. In fact Schneider reminds us that in the mosaic above the gate of the south vestibule depilating the last Byzantine Emperor Justinianus with the Virgin Mary and the Emperor Constantine.

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