Jerusalem reached a peak in size and population at the end of the Second Temple Period: The city covered two square kilometers (0.8 sq mi.) and had a population of 200,000. In the five centuries following the Bar Kokhba revolt in the 2nd century, the city remained under Roman then Byzantine rule. During the 4th century, the Roman Emperor Constantine I constructed Christian sites in Jerusalem such as the Church of the Holy Sepulchre.
In 603, Pope Gregory I commissioned the Ravennate Abbot Probus, who was previously Gregory's emissary at the Lombard court, to build a hospital in Jerusalem to treat and care for Christian pilgrims to the Holy Land. In 800, Charlemagne enlarged Probus' hospital and added a library to it, but it was destroyed in 1005 by Al-Hakim bi-Amr Allah along with three thousand other buildings in Jerusalem.
From the days of Constantine until the Arab conquest in 638, despite intensive lobbying by Judeo-Byzantines, Jews were forbidden to enter the city. Following the Arab capture of Jerusalem, the Jews were allowed back into the city by Muslim rulers such as Umar ibn al-Khattab.
During the 8th to 11th centuries, Jerusalem's prominence gradually diminished as the Arab powers in the region jockeyed for control.