On the south a less striking, but not less clearly defined, line--formed by the abutment of the upper and slightly elevated plain on the alluvium of the lower valley--separates Assyria from Babylonia, which is best regarded as a distinct country.

In the two remaining directions, there is more doubt as to the most proper limit.

Northwards,we may either view Mount Masius as the natural boundary, or the course of the Tigris from Diarbekr to Til, or even perhaps the Armenian mountain-chain north of this portion of the Tigris, from whence that river receives its early tributaries.

Westward, we might confine Assyria to the country watered by the affluents of the Tigris, or extend it so as to in elude the Khabour and its tributaries, or finally venture to carry it across the whole of Mesopotamia, and make it be bounded by the Euphrates.

On the whole it is thought that in both the doubted cases the wider limits are historically the truer ones.
Assyrian remains cover the entire country between the Tigris and the Khabour, and are frequent on both banks of the latter stream, giving unmistakable indications of a long occupation of that region by the great Mesopotamian people.