The Caliph al-Mansur founded the epicenter of the empire, Baghdad, in 762 CE, as a means of disassociating his dynasty from that of the preceding Umayyads (centered at Damascus) and the rebellious cities of Kufa and Basrah. Mesopotamia was an ideal locale for a capital city due to its high agricultural output, access to the Euphrates and Tigris Rivers (allowing for trade and communication across the region), central locale between the corners of the vast empire (stretching from Egypt to Afghanistan) and access to the Silk Road and Indian Ocean trade routes, all key reasons as to why the region has hosted important capital cities such as Ur, Babylon, Nineveh and Ctesiphon and was later desired by the British Empire as an outpost by which to maintain access to India.^[75] The city was organized in a circular fashion next to the Tigris River, with massive brick walls being constructed in successive rings around the core by a workforce of 100,000 with four huge gates (named Kufa, Basrah, Khorasan and Syria). The central enclosure of the city contained Mansur's palace of 360,000 square feet (33,000 m²) in area and the great mosque of Baghdad, encompassing 90,000 square feet (8,400 m²). Travel across the Tigris and the network of waterways allowing the drainage of the Euphrates into the Tigris was facilitated by bridges and canals servicing the population.^[76]