Constantine the Great probably does not get enough credit for being a strong military leader. He is remembered mostly for his adoption of Christianity as a religion and is work as emperor to protect Christians from persecution. Constantine was, however, a very successful general. The greatest empires that Constantine conquered were the two parts of the Roman Empire. When Constantine's father died in Britain, his army proclaimed Constantine a Caesar. Despite this claim, Constantine had to fight for the throne against political rivals. He defeated the emperor of the Western Roman Empire in 312 C.E. by marching on Rome. Constantine would defeat the Eastern Roman Empire in 324 C.E. and unify the entire empire under his governance.
Aside from conquering both sides of Rome, Constantine scored major victories over the Goths, Franks, and reclaimed the lost territory of Dacia.