Roman siege engines such as ballistas, scorpions and onagers were not unique. Animals depicted include onagers or zebras, ibexes, ostriches, lionesses, impalas, gazelles and cattle. Unlike most horses and donkeys, onagers have never been domesticated. The onagers of the Roman Empire were mainly used for besieging forts or settlements. They were hauled by onagers, related to donkeys. The invention of gunpowder weapons replaced only catapults and onagers; the change was slow. The Sumerian military used carts harnessed to onagers. Onagers and "aurochs" were planned to follow. Like all equids, onagers are herbivorous mammals. In India, mugger crocodiles can be great threats to onagers during migratory river crossings. The Turkmenian kulan is one of the largest subspecies of the onagers. Water is also found in the plants on which the onagers feed. Another interpretation is that he was a hunter of onagers. Currently, the biggest predator for onagers are gray wolves. Male onagers are usually larger than females.