NICOPOLIS AD ISTRUM. CAPUT AQUAE (Kalin Chakarov – kalinsbicke@abv.bg) The catchment of the western aqueduct of Nicopolis ad Istrum was explored in front of the entrance of the Musinska Peshtera Karst Cave. The catchment was constructed of 32 ashlars arranged in four courses, each one consisting of eight ashlars. There were П-like iron clamps, now missing, that held together the ashlars of the first and the second course. The inner size of the catchment was 4.23 m by 4.65 m and it was 2.20 – 2.40 m deep. There were two openings on its wall, the lower one connected to the main water-conduit of the aqueduct. The construction of caput aquae of the western aqueduct of Nicopolis ad Istrum could be dated to the reign of Hadrian. The temperature of the water from the Karst spring was 13.9°–14.1°С and during the explorations its capacity was c. 50 liters per second. A survey was carried out along the sections of the aqueduct located near the Villages of Musina, Dichin and Vodolei.