NICOPOLIS AD ISTRUM. CASTELLUM AQUAE (Ivan Tsarov – tsarov@abv.bg) The explorations of castellum aquae continued. The structure was 12.60 m by 12.50 m in size. Its bottom was paved with limestone ashlars held together with clamps. Building inscriptions with red-brown paint were documented on some ashlars. One inscription says: ΔΕΙΑ. The ashlars were laid over two courses of bricks. Six courses of uneven stones bonded with mortar were situated below the bricks. Nine rectangular barrel-vaulted chambers, built of bricks and stones bonded with mortar, were constructed under the courses of uneven stones bonded with mortar, at the lowest part of castellum aquae. The southeastern chamber was 3 m by 2.40 m in size and 1.56 m in height. One of the western chambers was 2.98 m by 2.42 m in size and 1.55 m in height. The chambers had structural function and were not accessible from the outside. A third water-conduit of terracotta pipes was discovered to the east of the cistern. An earlier midden pit of the 4th century AD, cut during the construction of the structure, was documented. The stratum related to the functioning of castellum aquae contained coins of AD 325 – 350. This is terminus post quem for the construction of the cistern, while terminus ante quem was AD 400 – 425. The previous hypothesis that castellum aquae was built in the 2nd century AD and later it was reconstructed is now rejected.