Charles Ellicott Commentary 2 Samuel 24:5

"And they passed over the Jordan, and encamped in Aroer, on the right side of the city that is in the middle of the valley of Gad, and unto Jazer:" — 2 Samuel 24:5 (ASV)

Pitched in Aroer. —The census began on the east of Jordan, at the extreme south, then passed northwards through the eastern tribes, and crossing the Jordan, passed southwards through the western tribes. Aroer is the city described in Deuteronomy 2:36; Joshua 13:16 as on the river Arnon, at the extreme southern border of the trans-Jordanian territory.

Of Gad. —This follows the Masoretic reading. It is better to put a period after the word river, and for “of Gad” to read “towards Gad.” Perhaps the words “and they came” (towards Gad) may have been lost from the text.

Jazer. —A boundary city of Gad (Joshua 13:25). From there they went to Gilead.