The basin of the Upper Narew River is home to one of the most interesting features connected with the early medieval Mazovian-Ruthenian borderland – the hillfort in Zbucz (site 3, AZP 45-89/4). It consists of an earthen embankment with a height of 1 to 2.5 m and average width of up to 10 m, surrounding a flat, 80-m-diameter courtyard entered from the south (Fig. 1, 2). During five excavation seasons, 10 trial trenches were explored and a non-invasive magnetic prospection was carried out (D. Krasnodębski, W. Małkowski 2018). The results obtained indicate two phases of construction of the fortifications. The main wood-and-earth rampart, reinforced from the outside with clay, was built in the 970s, then the fortifications were partially rebuilt no later than at the end of the 10th/beginning of the 11th century. Inside the hillfort, at the foot of the rampart, there was a shallow ditch in which small fragments of burnt human and animal bones were found. Moreover, several metal objects had been purposefully placed there: a bronze bracelet, a two-piece iron bit, an iron ‘horseshoe’, a C-shaped fire-steel, and two whole clay vessels (D. Krasnodębski, H. Olczak 2019, 95–96). This unusual collection of finds seems to indicate a special, perhaps cult/religious purpose for the ditch. On the outer side of the passageway leading to the hillfort, at a depth of about 0.7 m below the surface, a fragment of pavement (layer 234) formed by loosely distributed small stones embedded in clay was exposed directly on the virgin soil (Fig. 3–5). It is impossible to determine whether this pavement was located only within the gateway (meaning it would have to have been built during the construction of the rampart) or extended beyond it (thus being older than the hillfort). An incomplete fibula of group VI (Fig. 6), type A.161–162 (O. Almgren 1923, 77, pl. VII:161.162), with a narrow returned foot and a flat-convex section of the bow of 4.4 cm in length was found in this layer. Brooches type A.161–162 are found relatively frequently at Wielbark Culture sites in the Upper Narew and Middle Bug River basins. They are dated to the Late Roman Period – from phase C1a to C2 (K. Godłowski 1974, 29; R. Wołągiewicz 1974, 145; J. Jaskanis 1996, 111; J. Andrzejowski 2001, 257). This find is the only object from the Roman Period that has been discovered at the hillfort. Therefore, it cannot be ruled out that an older cemetery or settlement, heretofore unknown, existed within a short distance of the hillfort. It should also be taken into account that the layer of stones on which the fibula was found may be the remains of a sub-barrow pavement (cf. J. Jaskanis 2012, 210). However, the lack of human bones and other artefacts from the Roman Period speaks against this interpretation. It is also possible that the pavement with the brooch is a remnant of a destroyed cult enclosure, similar to the one discovered in the Białowieża Forest in 2017 (Forestry Wilczy Jar 2, AZP 45-91/28). It consists of a small hill dating from the middle of the 3rd to the beginning of the 5th century, measuring about 17 m in diameter, and surrounded by an earthen rampart faced with stones. A layer with loosely scattered stones and burnt debris, containing fragments of ceramics and small burnt animal bones, was found on its grounds. If we consider both described places to be similar, we can assume that the ceremonial and cult role of the hillfort in Zbucz in the early Middle Ages may date back to the late Roman times.