Rehoboam lived in Jerusalem and built up towns for defense in Judah:
References for 2 Chronicles 11:5
Bethlehem, Etam, Tekoa,
Beth Zur, Soco, Adullam,
Gath, Mareshah, Ziph,
Adoraim, Lachish, Azekah,
Zorah, Aijalon and Hebron. These were fortified cities1 in Judah and Benjamin.
References for 2 Chronicles 11:10
He strengthened their defenses and put commanders in them, with supplies of food, olive oil and wine.
He put shields and spears in all the cities, and made them very strong. So Judah and Benjamin were his.