The earliest migrations we can reconstruct from historical sources are those of the 2nd millennium BC. The Proto-Indo-Iranians began their expansion from c. 2000 BC, the Rigveda documenting the presence of early Indo-Aryans in the Punjab from the late 2nd millennium BC, and Iranian tribes being attested in Assyrian sources as in the Iranian plateau from the 9th century BC. In the Late Bronze Age, the Aegean and Anatolia were overrun by moving populations, summarized as the "Sea Peoples", leading to the collapse of the Hittite Empire and ushering in the Iron Age.