The Muslim conquest of Egypt, also known as the Rashidun conquest of Egypt, led by the army of 'Amr ibn al-'As, took place between 639 and 646 and was overseen by the Rashidun Caliphate. It ended the seven centuries long period of Roman/Byzantine reign over Egypt that began in 30 BCE. Byzantine rule in the country had been shaken, as Egypt had been conquered and occupied for a decade by the Sassanid Iran in 618–629, before being recovered by the Byzantine emperor Heraclius. The caliphate took advantage of Byzantines' exhaustion and captured Egypt ten years after its reconquest by Heraclius. During the mid-630s, Byzantium had already lost the Levant and its Ghassanid allies in Arabia to the Caliphate. The loss of the prosperous province of Egypt and the defeat of the Byzantine armies severely weakened the empire, resulting in further territorial losses in the centuries to come.