Complex sentence: Otto III was crowned as king on Christmas Day 983, three weeks after his father's death, by Willigis, the Archbishop of Mainz, and by John, the Archbishop of Ravenna.
Split into simpler sentences: Otto III was crowned as king on Christmas Day 983, three weeks after his father's death. He was crowned by Willigis, the Archbishop of Mainz, and by John, the Archbishop of Ravenna.