Unlike the Akkadians and Assyrians, whose Anatolian trading posts were peripheral to their core lands in Mesopotamia, the Hittites were centered at Hattusa (modern Boğazkale) in north-central Anatolia by the 17th century BC. They were speakers of an Indo-European language, the Hittite language, or "nesili" (the language of Nesa) in Hittite. The Hittites originated from local ancient cultures that grew in Anatolia, in addition to the arrival of Indo-European languages. Attested for the first time in the Assyrian tablets of Nesa around 2000 BCE, they conquered Hattusa in the 18th century BCE, imposing themselves over Hattian- and Hurrian-speaking populations. According to the widely accepted Kurgan theory on the Proto-Indo-European homeland, however, the Hittites (along with the other Indo-European ancient Anatolians) were themselves relatively recent immigrants to Anatolia from the north. However, they did not necessarily displace the population genetically; they assimilated into the former peoples' culture, preserving the Hittite language.