In the late Roman period, Egypt is known as the Byzantine Egypt or the Coptic period since the reign of the Roman Emperor Diocletian in 284 AD until the Arabs conquest of Egypt in 641 AD. The reign of Emperor Diocletian witnessed the most aggressive persecutions in the Roman history, especially against the Egyptian Christians. The Copts chose the year of Diocletian's ascension to the throne as the beginning of their calendar, which was called the calendar of martyrs. The Egyptian Christians suffered persecution until the Edict of Milan's issuance in 313 AD in which Christianity was granted equal rights to other religions by Emperor Constantine I, who ruled the Western Roman Empire. In 324 AD Constantine I defeated Licinius, the ruler of the Eastern Roman Empire, and Constantine I became the only Emperor of the Roman Empire who transferred the headquarters to the new Capital Constantinople after its foundation in 330 AD.