At the commencement of the Muslim conquest of Egypt, Egypt was part of the Byzantine/Eastern Roman Empire, which had its capital at Constantinople. Egypt had been conquered just a decade before by the Persian Empire under Khosrau II (616 to 629 AD); however, Emperor Heraclius re-captured it after a series of campaigns against the Sassanid Persians, only to lose it to the Muslim Rashidun army ten years later. Before the Muslim conquest of Egypt had begun, the Byzantines had already lost the Levant and its Arab ally, the Ghassanid Kingdom, to the Muslims. All of this left the Byzantine Empire dangerously exposed and vulnerable.