The assemblage of copper alloy objects presented in the article comes from a series of random discoveries made around 2005 in the farmland between Sieluń and Dyszobaba (both, villages in Maków Mazowiecki County), lying to the west of Lake Sieluńskie and the river Róż which flows from the lake on its south side (Fig. 1). Except for a plate-headed brooch now in the regional museum (Muzeum Ziemi Zawkrzeńskiej) in Mława (inv. no. A/1432), all these objects are at present held by the State Archaeological Museum in Warsaw (inv. no. IV/10481). Almost all of these finds may be attributed to Wielbark Culture settlement. The earliest of them (phases B2/C1 and C1) are a fragmented brooch, Almgren group V series 8 (Fig. 2:1) and an incomplete brooch with a high catchplate, a so-called Sarmatian variant (Fig. 2:3). The other finds date to the mature phase C of the Roman Period and to the Early Migration Period: next to the relatively common brooches type A 172 (Fig. 2:5.6) and a buckle similar to types AH14-15 of R. Madyda-Legutko (Fig. 2:9) there are also forms unique or only rarely present in Wielbark Culture deposits. Definitely in the first of these categories is an object of obscure function (Fig. 2:4), which has a profiling analogical to unipartite brooches with a closed catchplate known from Moravia and western Slovakia dated to phases C3–D. The second category is represented by a caterpillar brooch, I series, of M. Tuszyńska (Fig. 2:7), and a plate-headed brooch, group B of A. Kokowski (Fig. 2:8). According to the recently published archival material (A. Bitner-Wróblewska, A. Rzeszotarska-Nowakiewicz, T. Nowakiewicz 2011) brooches with a corrugated bow and a head not provided with either a knob, a plate or a projection are encountered most often on the territory of Balt cultures, more rarely, on the territory of Wielbark Culture. The preservation of the brooch from Sieluń is too poor to determine the form of its foot. It could have been rectangular, as in most specimens known to us, but it is also possible that, similarly as the brooch from grave 100B from Cecele, Siemiatycze County, the foot was lozengic. Plate-headed brooches are forms characteristic for southern Gothic cultures. In the region to the north of the Carpathians their finds are relatively rare. The specimen from Sieluń differs a little from similar brooches known from the territory of the Masłomęcz Group and Balt cultures by having an upper, rather a lower, cross-bow shaped XX, secured by means of a special notch in the plate in which the axis of the spring is fixed. A similar design of the fastening is seen in plate-headed brooches from Ukrainian finds, some of them forms similar to group B. With a diameter of 28 mm the ring (Fig. 2:2) is interpreted as a belt fitting and cannot be dated more closely – similar forms are known both from the Early and the Late Roman Period. At the present stage of inquiry it is hard to conclude whether the artifacts from Sieluń are settlement or grave finds. The first possibility would be supported by the absence of cremated bone and preservation – none of these metal objects had been affected by fire. At the same time there is no evidence that during the period of interest the area was suitable for settlement – the level of the farmland at Sieluń, site of discovery of our group of artifacts, had an elevation only a little higher than the water level in the nearby lake and river (Fig. 1). Without test trenching and specialist geological studies we cannot hope to resolve this question. Regardless of the character of the site at Sieluń it may definitely be regarded as evidence on Wielbark Culture settlement in a part of Mazowsze which until recently used to be viewed as an area mostly lacking in Wielbark Culture finds. The same farmland at Sieluń also yielded the find of a silver Celtic coin, type Simmering, unique for the area to the north of the Carpathians, struck around mid-1st century BC. It may be attributed to Przeworsk Culture settlement of phase A3 of the Late Pre-Roman Period, possibly even phase B1 of the Early Roman Period (J. Andrzejowski, w druku).