Mesopotamia was known as "The land between the rivers", which was a name given by Polybius and Strabo of the lands lying between the Tigris and the Euphrates rivers.

The north borders are the mountains of Kurdistan.

The south borders are the marshes of the river delta.

The west borders are the Syrian steppes and deserts.

The east borders are the mountains of Iran.

Though the northern and southern parts of Mesopotamia differ in many ways (geographically, culturally, etc) they can still be considered as two facets of the same historical entity that can properly be referred to as Mesopotamia throughout their cultural development, which lasts from the beginning of the third millennium BC, down to the end of the Persian period.