Peoples belonging to numerous archeological cultures identified with Celtic, Germanic and Baltic tribes inhabited parts of Poland during the era of classical antiquity, from about 400 BC to 450-500 AD. Other groups, difficult to identify, were most likely also present, as the ethnic composition of archeological cultures is often poorly recognized. Short of using a written language to any appreciable degree, many of them developed a relatively advanced material culture and social organization, as evidenced by the archeological record, for example by richly furnished, dynastic "princely" graves. Characteristic of this period were high rates of migration, often involving large groups of people.