Excerpts from Books and Wikipedia
"Nineveh (...) was an ancient Assyrian city of Upper Mesopotamia, located on the outskirts of Mosul in modern-day northern Iraq. It is located on the eastern bank of the Tigris River, and was the capital of the Neo-Assyrian Empire. Today it is a common name for the half of Mosul that lies on the eastern bank of the Tigris.
It was the largest city in the world for some fifty years until the year 612 BC when, after a bitter period of civil war in Assyria, it was sacked by a coalition of its former subject peoples, the Babylonians, Medes, Chaldeans, Persians, Scythians and Cimmerians. . . . It was Sennacherib who made Nineveh a truly magnificent city (c. 700 BC). He laid out new streets and squares and built within it the South West Palace . . . The Book of Jonah depicts Nineveh as a wicked city worthy of destruction. God sent Jonah to preach to the Ninevites of their coming destruction, and they fasted and repented because of this. As a result, God spared the city; " [Wikipedia]