Complex sentence: Those people that were traitors to the army, enemies of the empire and criminals were crushed by the elephants this way and executed in the age of Sassanids they also used this method of execution for training for battle.
Split into simpler sentences: Those people that were traitors to the army, enemies of the empire, and criminals were crushed by the elephants this way in the age of Sassanids. They also used this method of execution for training for battle.