SOSTRA (Ivan Hristov – ivchristov70@abv.bg) Excavations were carried out in Sector III of Castellum Sostra, situated on the Roman road Ulpia Oescus – Philippopolis. Building No. 7 was explored, situated close to the southern fortification gate, adjoining the northern wall of the western tower. The building measured 15 m by 10 m and was two-storey. It had four rooms on the ground floor with walls built in rubble masonry and preserved up to 2 m in height. Its foundations were dug into a stratum of AD 150 – 250. Building No. 7 was constructed after the southern fortification wall was built after the AD 270s. Judging from the coins and the pottery, the building existed until the end of the 4th – first half of the 5th century AD.