Assyria, one of the great empires of the ancient world, located in western Asia. Assyria originally encompassed only the foothill region between the Tigris River and the Zagros Mountains (now northern Iraq). At the height of its power, in the seventh century B.C., the Assyrian empire stretched from Urartu (later Armenia) in the north to Egypt in the south, and from the Persian Gulf on the east to the Mediterranean Sea on the west. Nineveh, on the upper Tigris, was its capital.