NET
21 Now all Moab had heard that the kings were attacking, so everyone old enough to fight was mustered and placed at the border.
Darby
21 And all the Moabites heard that the kings were come up to fight against them, and they were called together, all that were able to put on armour, and upward, and stood by the border.
KJV
21 And when all the Moabites heard that the kings were come up to fight against them, they gathered all that were able to put on armour, and upward, and stood in the border.