The Bastarnae, Bastarni or Basternae, also known as the Peuci or Peucini, were an ancient people who are known from Greek and Roman records to have inhabited areas north and east of the Carpathian Mountains between about 300 BC and about 300 AD, stretching in an arc from the sources of the Vistula in present-day Poland and Slovakia, to the Lower Danube, and including all or most of present-day Moldava. The Peucini were sometimes described as a subtribe, who settled the Peuke Island in the Danube Delta, but apparently due to their importance their name was sometimes used for the Bastarnae as a whole. Near the sources of the Vistula another part of the Bastarnae were the Sidones, while the Atmoni, another tribe of the Bastarnae are only mentioned in one listing by Strabo.
The earliest Graeco-Roman historians to refer to the Bastarnae imply that they were culturally Celtic. Also consistent with connections to the cultures to their west, later Roman-era sources state directly that they spoke Germanic languages, and could be considered Germanic peoples. In contrast, like other peoples who lived in this geographical region, Graeco-Roman writers also sometimes referred to the Bastarnae as a "Scythian" or "Sarmatian" people, but this was a reference to their location, and customs, rather than a linguistic category. Although largely sedentary, at least one Roman writer, Tacitus, stated that the Bastarnae had adopted some Sarmatian customs. So far, no archaeological sites have been conclusively attributed to the Bastarnae. The archaeological horizon most often associated by scholars with the Bastarnae is the Poieneşti-Lucașeuca culture.