Complex sentence: At Aleth, opposite St Malo, Malo placed himself under a venerable hermit named Aaron, on whose death in 544, he succeeded to the spiritual rule of the district subsequently known as St Malo, and was consecrated first Bishop of Aleth.
Split into simpler sentences: At Aleth, opposite St Malo, Malo placed himself under a venerable hermit named Aaron. Upon Aaron's death in 544, Malo succeeded to the spiritual rule of the district subsequently known as St Malo and was consecrated first Bishop of Aleth.