Around 3500–3000 BCE, horse bones began to appear more frequently in archaeological sites beyond their center of distribution in the Eurasian steppes and were seen in central Europe, the middle and lower Danube valley, and the North Caucasus and Transcaucasia. Evidence of horses in these areas had been rare before, and as numbers increased, larger animals also began to appear in horse remains. This expansion in range was contemporary with the Botai culture, where there are indications that horses were corralled and ridden. This does not necessarily mean that horses were first domesticated in the steppes, but the horse-hunters of the steppes certainly pursued wild horses more than in any other region. This geographic expansion is interpreted by many zoologists as an early phase in the spread of domesticated horses.