John Gill Commentary 2 Chronicles 11:12

"And in every city [he put] shields and spears, and made them exceeding strong. And Judah and Benjamin belonged to him." — 2 Chronicles 11:12 (ASV)

And in every several city he put shields and spears
Furnished them with these and perhaps other pieces of armour, these being put for all, to defend themselves with against an enemy, and to annoy them:

and made them exceeding strong ;
so that they could not be easily taken:

having Judah and Benjamin on his side :
which tribes cleaved to one another, and to Rehoboam, and to the kings of the house of David, in later times, as well as to the true religion.