ARCHAEOLOGICAL EXPLORATIONS IN SERDICA (Konstantin Shalganov – director@sofiahistorymuseum.bg) Parts of two rooms were explored. Most probably, they belonged to the Roman Thermae of Serdica situated to the south of the northern fortification gate, close to the mineral thermal spring. Room No. 1 was polygonal (probably octagonal), preserved up to 2.20 m in height and built of bricks, 33/34 cm by 33/34 cm by 4/4.5 cm in size, bonded with mortar. There was a vaulted corridor, 2.32 m wide and 2 m high, in the southern wall of the room. Room No. 1 probably had a pavement of stone slabs. Room No. 2 was semicircular, preserved up to 3 m in height, 4.56 m in diameter and 1.91 m in radius. The southern wall was 60 cm wide. The structure of the room was not homogeneous: it was built of courses of bricks with different height and length, mixed with identical courses of boulders. A semicircular pool was explored in the room. The pool was 4.42 m in diameter and 1.84 m n radius. Its walls were faced with marble veneer, consisting of rectangular panels, 70 cm by 30 cm by 1 cm in size. The bottom of the pool was paved with marble plates. Both rooms dated to the 4th – 6th centuries AD.