The Battle of Nahavand was fought in 642 between the Rashidun Muslim forces under caliph Umar and Sasanian Persian armies under King Yazdegerd III. Yazdegerd escaped to the Merv area, but was unable to raise another substantial army. It was a victory for the Rashidun Caliphate and the Persians consequently lost the surrounding cities including Spahan (Isfahan). The former Sassanid provinces, in alliance with Parthian and White Hun nobles, resisted for about a century in the region south of the Caspian Sea, even as the Rashidun Caliphate was replaced by the Umayyads, thus perpetuating the Sassanid court styles, Zoroastrian religion, and Persian language.