The Sassanid Persian empire had been a rival of Byzantium since the early 4th century AD. Wars between the two nations had never been particularly sanguinary affairs and in the end the Persian hegemony over the Iranian Plateau and the surrounding lands was destroyed by the Arab Rashidun Caliphate. The battles of Qadisiya and Nehavend ensured Persia's defeat and Iran's brief incorporation into the Rashidun Caliphate. An Persian enclave survived as the Principality of Merv, which later became a Khazar protectorate.