The territories of the Ottoman empire intersected with what geographers refer to as the ‘sub-Arctic nomadic zone’, which extended from the Mediterranean littoral, through the Anatolian peninsula and the Iranian plateau, on to the mountains of Central Asia. For millennia, tens of thousands of tribes moved constantly across this belt of high mountains and dry steppes and deserts. Starting in the eleventh century, Turkic and Mongolian tribes arrived in Anatolia and eastern Mediterranean lands. They became integrated into the indigenous patterns of circulation and altered forever the social and political make-up and the history of these regions. As they passed through these lands, these tribes interacted with local communities; some melded into local relations and networks and abandoned their journey, while others continued to move. Superimposition of the long-distance migrations onto local structures and movements created a highly fluid social environment throughout this territory. Especially in Anatolia, between the eleventh and fourteenth centuries it became difficult to distinguish between the arriving, staying, or departing tribes, let alone between sedentary and nomadic communities. This was the context within which the Ottoman empire grew to become a world empire after the thirteenth century.