In July or August of 614 BC, the Medes began attacking the cities of Kalhu and Nineveh. They then besieged Assur, the ancient political (and still religious) heart of Assyria. The siege was successful and the city endured a brutal sack.
Despite the sorely depleted state of Assyria, bitter fighting ensued; throughout 614 BC the Medes continued to gradually make hard-fought inroads into Assyria itself, scoring a decisive and devastating victory over the Assyrian forces at the battle of Assur.