During the Byzantine period, in the years between Constantine the Great's rise to power (324 AD) and the conquest of Jerusalem by the Rashidun Caliphate in 637, Jerusalem was under the control of the Byzantine Empire. The essential change in the character and status of the city, compared to the Roman period, was its transformation from a pagan city to a Christian city. The Byzantine rule developed the Roman colony Aelia Capitolina in Jerusalem, turning it into a central Christian city from a religious and administrative point of view (with the administration subject to the institutional-religious hierarchy) and a world center for pilgrimage. At the end of the period, between the years 614–628, Jerusalem was conquered by the Sasanian Empire, but was later recaptured by Byzantine Christians in 629 CE. Jerusalem was captured by the Rashidun Caliphate in 637 CE as part of the Siege of Jerusalem (636–637).