Erbil, also called Hawler, is the capital and most populated city in the Kurdistan Region of Iraq. The city is the capital of the Erbil Governorate. Human settlement at Erbil may be dated back to the 5th millennium BC. At the heart of the city is the ancient Citadel of Erbil and Mudhafaria Minaret. The earliest historical reference to the region dates to the Third Dynasty of Ur of Sumer, when King Shulgi mentioned the city of Urbilum. The city was later conquered by the Assyrians.