He inhabited - i. e. Reuben. Eastward the Reubenites inhabited as far as the commencement of the great Syrian Desert, which extended all the way from the river Euphrates to their borders.
SDA Bible Commentary (limited)
Volume 1-7
9. The wilderness. As the Reubenites increased they continued to push to the east, to the great desert between Transjordan and the Euphrates.