Complex sentence: At the prompting of Pope Leo I he convened the seventh Council of Milan in 451; he is also known for his work in rebuilding the cathedral following the sack of Milan at the hands of Attila and the Huns in 452.
Split into simpler sentences: At the prompting of Pope Leo I he convened the seventh Council of Milan in 451. He is also known for his work in rebuilding the cathedral following the sack of Milan at the hands of Attila and the Huns in 452.