From ca. 400 onwards, a late Roman private bath was built near the aqueduct bridge, only 1.30 m away from the bridge pier. It existed up to the early sixth century, when it was demolished. A part of this Roman bath was covered by a Byzantine church, built adjacent to the aqueduct bridge itself. Today, these Roman baths and the present-day building are part of the Kalenderhane Mosque.
The bath had multiple rooms, of which the foundations can still be seen today:
Room A (surviving outside): hypocaust (heated) floor.
Room B: circular room adjacent to Room A, now partially overbuilt during the Church phase.
Room C: circular room west of Room B. Its hypocaust floor was destroyed by the construction of a canal.
Room D: little evidence.
Under these rooms ran five channels, and terracotta pipes have been found. How the water system within the bath actually worked, remains obscure.
