Peoples belonging to numerous archeological cultures identified with Celtic, Germanic and Baltic tribes, lived and migrated through various parts of the territory that now constitutes Poland in Antiquity, an era that dates from about 400 BC to 450–500 AD. Other groups, difficult to identify, were most likely also present, as ethnic composition of archeological cultures is often poorly recognized. Short of using a written language to any appreciable degree, many of them developed relatively advanced material culture and social organization, as evidenced by the archeological record, for example judged by the presence of richly furnished, dynastic "princely" graves. Characteristic of the period was high geographical migration rate of large groups of people, even equivalents of today's nations. This article covers the continuation of the Iron Age (see Bronze and Iron Age Poland), the La Tène and Roman influence and Migration periods. La Tène period is subdivided into La Tène A, 450 to 400 BC; La Tène B, 400 to 250 BC; La Tène C, 250 to 150 BC; La Tène D, 150 to 0 BC. 400 to 200 BC is also considered the early pre-Roman period and 200 to 0 BC the younger pre-Roman period (A). It was followed by the period of Roman influence, of which the early stage had lasted from 0 to 150 AD (0–80 B1, 80–150 B2), and the late stage from 150 to 375 AD (150–250 C1, 250–300 C2, 300–375 C3). 375 to 500 AD constituted the (pre-Slavic) Migration Period (D and E).
The Celtic peoples established a number of settlement centers, beginning in the early 4th century BC, mostly in southern Poland, which was at the outer edge of their expansion. Through their highly developed economy and crafts, they exerted lasting cultural influence disproportional to their small numbers in the region.
Expanding and moving out of their homeland in Scandinavia and northern Germany, the Germanic peoples had lived in today's Poland for several centuries, during which period many of their tribes also migrated out in the southern and eastern directions (see Wielbark culture). With the expansion of the Roman Empire, the Germanic tribes came under the Roman cultural influence. Some written remarks by Roman authors that are relevant to the developments on Polish lands have been preserved; they provide additional insight when compared with the archeological record. In the end, as the Roman Empire was nearing its collapse and the nomadic peoples invading from the east destroyed, damaged or destabilized the various Germanic cultures and societies, the Germanic people left eastern and central Europe for the safer and wealthier southern and western parts of the European continent.
The northeast corner of contemporary Poland's territory was and remained populated by Baltic tribes. They were at the outer limits of significant cultural influence of the Roman Empire.