1 Chronicles 19:6-10

When the sons of Ammon saw that they had made themselves repulsive to David, Hanun and the sons of Ammon sent a thousand talents of silver to hire for themselves chariots and horsemen from Mesopotamia, Aram-maacah, and Zobah.

So they hired for themselves thirty-two thousand chariots, and the king of Maacah and his people, who came and camped opposite Medeba. And the sons of Ammon gathered together from their cities and came to the battle.

When David heard about it, he sent Joab and all the army, the mighty men.

The sons of Ammon came out and drew up in battle formation at the entrance of the city; and the kings who had come were by themselves in the field. Ammon and Aram Defeated

Now when Joab saw that the battle was set against him at the front and at the rear, he selected warriors from all the choice men in Israel and lined them up against the Arameans.