A further expansion, into the lowland Near East and northwestern China, also happened around 2000 BCE, again apparently in conjunction with the chariot. Although "Equus" bones of uncertain species are found in some Late Neolithic sites in China dated before 2000 BCE, "Equus caballus" or "Equus ferus" bones first appeared in multiple sites and in significant numbers in sites of the Qijia and Siba cultures, 2000–1600 BCE, in Gansu and the northwestern provinces of China. The Qijia culture was in contact with cultures of the Eurasian steppes, as shown through similarities between Qijia and Late Bronze Age steppe metallurgy, so it was probably through these contacts that domesticated horses first became frequent in northwestern China.