The Battle of Nahavand, also spelled Nihavand or Nahawand, was fought in 642 between the Rashidun Muslim forces under An-Numan ibn Muqarrin and Sasanian army under King Yazdegerd III. Yazdegerd escaped to the Merv area, but was unable to raise another substantial army. The battle ended in a victory for the Rashidun Caliphate and the Sasanids consequently lost the surrounding cities including Spahan (Isfahan). The engagement resulted in a catastrophic defeat for the Sasanid forces and marks the end of organized Sasanid resistance. Thus opening the path for Islamic expansion into Persia and the subsequent religious transformation of the region.