Ellasar

the oak or heap of Assyria, a territory in Asia of which Arioch was king (Gen 14:1 ; 14:9). It is supposed that the old Chaldean town of Larsa was the metropolis of this kingdom, situated nearly half-way between Ur (now Mugheir) and Erech, on the left bank of the Euphrates. This town is represented by the mounds of Senkereh, a little to the east of Erech.

EBD - Easton's Bible Dictionary