 Complete the following phrase:  The earliest historical reference to the region dates to the Ur III dynasty, when king Shulgi mentioned the city of Urbilum  the ancient name of modern-day Erbil. The great Assyrian capitals of Assur, Nineveh, Nimrud and Dur-Sharrukin were all located in the foothill zone where the Great Zab flows into the Tigris, and the Great Zab basin became increasingly integrated into the Middle Assyrian and Neo-Assyrian empires. Nimrud, the capital of the empire until 706 BCE, was located only away from the confluence of the Great Zab with the Tigris. The Assyrian king Ashurnasirpal II constructed a canal called Patti-Hegalli that tapped water from the Great Zab to irrigate the land around Nimrud, and this canal was restored by his successors Tiglath-Pileser III and Esarhaddon. This canal ran along the right bank of the Great Zab and cut through a rock bluff by means of a tunnel and is still visible today. After the fall of the Neo-Assyrian empire, the Medes gained control of the area, followed by the Achaemenids in 550 BCE. The 