The remains of the Billingsgate house and baths in Lower Thames Street were first discovered in 1848 during the construction of the Coal Exchange and the remains, preserved and displayed in the basement, were scheduled in the first Ancient Monuments Act of 1882. Further discoveries were made during excavations carried out in 1967-70 when the Coal Exchange and neighbouring buildings were demolished and Lower Thames Street widened.
The house was probably first built in the late 2nd century. At this date, it would have had a waterfront location with easy access to the river. It was a winged building with a north and east wing (and perhaps a west wing although no evidence remained of this), with rooms connected by a corridor or verandah which connected the rooms in the east wing with those of the north. The rooms in the surviving east wing had underfloor heating and allowed hot air to circulate underneath the floor and up the walls.
The house took its final form in the 3rd century when the bath-house was added in the open yard to the front. It consisted of a cold room (frigidarium - shown blue here), a warm room (tepidarium - orange) and a hot room (caldarium - red). Hot air to provide heating for both buildings came from furnaces (shown on the plan with red stars) set directly outside the buildings. See an enlarged plan of the house and baths.
Only the east wing and baths continued in use and a scatter of late Roman coins (dating to AD388 and later), found in the furnace room, indicate that these rooms remained in use into the 5th century. By the mid 5th century, however, although the walls were still standing, the roof had collapsed in both buildings, sending roof tiles crashing to the floor. Not long after, a Saxon visitor dropped her brooch amongst the roof debris that had collapsed onto the floor of the baths.
The remains at Billingsgate are important in understanding the fate of late Roman London as it is only one of a few recorded buildings to continue in use into the 5th century. It is also a rare survival of a building in situ in the City of London.
For further information on London's other baths, see Public baths in Public life.