Offa had diplomatic relations with Charlemagne. He was one of the few Anglo-Saxon monarchs to have dealings with continental rulers. Letters and presents were exchanged. But when Offa sought a marriage of his son to one of Charlemagne's daughters, relations were quickly cut off. Charlemagne had all Frankish ports closed to British ships. Offa, very involved in church affairs, presided over church councils personally in 786-7. In 787 he convinced the pope to create the position of archbishop of Lichfield in Mercia. He wanted his own archbishop who was closer at hand than the Archbishop of Canterbury. He reorganized the defenses of his kingdom. One of these defenses, Offa's Dyke was a massive earthworks between Mercia and the Welsh kingdoms to the west. Offa died in 796. His son, Ecgfrith, lasted only 141 days as king. Mercia was never again as powerful as it was during Offa's reign.