Beyazıt Churches A, B and C
Ruins of Beyazıt Churches A, B and C were located west of the Forum of Theodosius. Theirs ruins are currently located under some of the buildings of the Istanbul University. It is possible that all of them were built in the 6th century, though the date of Church C in particular is disputed. It is possible that these churches can be identified as the Theotokos of Diakonissa. They were discovered following a fire that destroyed the 19th century Zeynep Kâmil Konak in 1942 and the subsequently construction of an annex building for Istanbul University in the 1940s.
Church A had a nave with a single aisle on either side. Three column bases discovered in situ have incisions that suggest that there were screens dividing the nave from the aisles at the ground level. The column bases supported columns of Thessalian marble. Three Ionic basket capitals were found on location, evidently belonging to them. Pilaster columns of a similar type were also found, of which Justinian’s Hagia Sophia provides excellent parallels. The sculptural evidence suggests an early 6th century date. 
Church C was located immediately north of Church A. There was a cistern underneath the courtyard between the churches, measuring 4.96 x 2.80 meters. An opening in the courtyard suggests it was open to the sky and that this cistern stored rainwater. The church had an exonarthex and a narthex. Its nave was about 11 meters wide and its aisle 9.5 meters long. The details of the plan and its date have been debated. 
Church B was 1.5 meters higher than Church C. It could be due to the topography, though it also might suggest a later date. It seems to be best categorized as a ‘compact dome basilica’, measuring 13 x 19 meters. Just north of Church B was a cistern measuring 15.5 x 9 meters (with a depth of 5 meters). Several 2nd century tombs were also discovered in the vicinity of the church ruins.