al-Ma'mun's Anatolian campaign

Al-Mas'udi relates that al-Ma'mun raided the land of the Byzantines in 218 AH, having begun building the fortress of al-Tuwana at the mouth of the pass on the side toward Tarsus. ²

The Byzantine king sent an envoy with a letter giving him the choice between repaying his expenses, releasing every Muslim captive, or rebuilding what Christianity had destroyed. Al-Ma'mun prayed two rak'as and asked God for guidance, then sent the three terms back and said that there was nothing between him and the king but the sword. ²

He took fifteen fortresses, then camped at the spring of al-Badidun, where he died. ²