Complex sentence: In the Centaur battle, Caeneus proved invulnerable, until the Centaurs simply crushed him with rocks and trunks of trees, he disappeared into the depths of the earth unharmed and was released as a sandy-headed bird.
Split into simpler sentences: In the Centaur battle, Caeneus proved invulnerable, until the Centaurs simply crushed him with rocks and trunks of trees. He disappeared into the depths of the earth unharmed and was released as a sandy-headed bird.