Christians) essentially secularized the city. The ban was maintained until the 7th century, though Christians would soon be granted an exemption: during the 4th century, the Roman emperor Constantine I ordered the construction of Christian holy sites in the city, including the Church of the Holy Sepulchre. Burial remains from the Byzantine period are exclusively Christian, suggesting that the population of Jerusalem in Byzantine times probably consisted only of Christians. In the fifth century, the eastern continuation of the Roman Empire that was ruled from Constantinople, maintained control of the city. At the beginning of the seventh century, within the span of a few decades, the city shifted from Byzantine to Persian rule, then back to Roman-Byzantine dominion. Following Sassanid Khosrau II's early seventh century push through Syria, his generals Shahrbaraz and Shahin attacked Jerusalem () aided by the Jews of Palaestina Prima, who had risen up against the Byzantines. In the Siege of Jerusalem of 614 AD, after 21 days of relentless siege warfare, Jerusalem was captured. Byzantine chronicles relate that the Sassanids and Jews slaughtered tens of thousands of Christians in the city, many at the Mamilla Pool, and destroyed their monuments and churches, including the Church of the Holy Sepulchre. The conquered city would remain in Sassanid hands for some fifteen years until the Byzantine emperor Heraclius reconquered it in 629. Byzantine Jerusalem was conquered by the Arab armies of Umar ibn al-Khattab in AD 638, which resulted in the removal of the restrictions on Jews living in the city. Among Muslims of Islam's earliest era it was referred to as Madinat bayt al-Maqdis, 'City of the Temple', a name restricted to the Temple Mount. The rest of the city was called "Iliya", reflecting the Roman name Aelia Capitolina. Plan of the city The city was without walls, protected by a light garrison of the Tenth Legion, during the Late Roman period. The detachment at Jerusalem, which apparently encamped all over the city's western hill, was responsible for preventing Jews from returning to the city. Roman enforcement of this prohibition continued through the 4th century. Layout and street pattern The urban plan of Aelia Capitolina was that of a typical Roman town wherein main thoroughfares crisscrossed the urban grid lengthwise and widthwise. The urban grid was based on the usual central north–south road (cardo maximus) and central east–west route (decumanus maximus). However, as the main cardo ran