Mosul is a major city in northern Iraq, serving as the capital of Nineveh Governorate. The city is considered the second largest city in Iraq in terms of population and area after the capital Baghdad, with a population of over 3.7 million. Mosul is approximately 400 km north of Baghdad on the Tigris river. The Mosul metropolitan area has grown from the old city on the western side to encompass substantial areas on both the "Left Bank" and the "Right Bank", as locals call the two riverbanks. Mosul encloses the ruins of the ancient Assyrian city of Nineveh – once the largest city in the world – on its east side.