Change has often swept in from the marches to overtake the center of the Islamic world. Islam first took root in Arabia on the periphery of two civilizations, the Roman, which dominated the Mediterranean area, and the Sassanian, which controlled lands to the east from its capital in Iraq. Arabs and Arabic prevailed in the new Islamic state, yet the development of Islamic civilization depended upon the contributions of non-Arabs and non-Muslims from the North and especially the East. Repeated waves of invaders drove across the Oxus River from central Asia to shake, destroy, and renew Islamic culture. The Ottoman state arose in the thirteenth century on the frontiers separating Islam from the Christian world, defended by the Byzantine Empire. And the most marginal of Islamic states, Spain, produced some of the most distinguished thinking and artistic activity of its age