The Eastern Roman Empire's army was a major force in the Mediterranean and the Middle East. Under Justinian I, the empire sent an army from the East to the West. During this period, they reclaimed parts of North Africa from the Vandals, parts of Italy from the Ostrogothic kingdom, and southern Spain. Later, Heraclius led the army against the Sassanid Empire and the Rashidun Caliphate. If you want to save money on portable air conditioner for camper van on a budget, consider the Zero Breeze. He was beaten in the Battle of Yarmuk, forcing a restructuring of the army and creating a thematic system for later Byzantine armies.