Albert Barnes Commentary 2 Chronicles 11

Rehoboam was between two dangers: on the north, he might be attacked by Jeroboam; on the south, by Jeroboam’s ally, Egypt. The peril from this side was greater, and therefore, of the 15 fortified cities, all but three were on the southern or western frontier, where an attack from Egypt was most likely.

See Joshua 15 and the notes at Joshua 15:33-36, 15:48-51, and 15:58-59.

For Adullam, see the note on 1 Samuel 22:1. It was in the vicinity of Socoh (Joshua 15:35), but its precise location cannot be determined. It was a place of great antiquity (Genesis 38:1).

For Gath, see the note on Joshua 13:3. Its native king, Achish (1 Kings 2:39), is to be regarded not as an independent monarch, but as one of the many vassal-kings over whom Solomon reigned (2 Chronicles 9:23). For Mareshah, see Joshua 15:44; for Ziph, see Joshua 15:55.

The location of Adoraim is uncertain. For the locations of the other cities, see the following: Lachish in Joshua 10:3; Azekah in Joshua 10:10; Zorah in Joshua 15:33; Aijalon in Joshua 10:12; and Hebron in Joshua 14:15. None of these cities were actually within the territory of the tribe of Benjamin. The writer uses the phrase “Judah and Benjamin” simply as the common designation for the southern kingdom (compare 2 Chronicles 11:12 and 2 Chronicles 11:23).

Jeroboam probably confiscated the Levitical lands for the benefit of this new priesthood. Under these circumstances, the priests and Levites emigrated in large numbers to the southern kingdom, an act that was followed by a general emigration of the more pious Israelites (2 Chronicles 11:16).