1 Chronicles 19:9

And the children of Ammon came out, and put the battle in array before the gate of the city: and the kings that were come were by themselves in the field.

Children of Ammon ... put the battle in array before the gate of the city - i:e., outside the walls of Medebah, a frontier town on the Arnon.

The kings that were come were by themselves in the field. The Israelite army being thus beset by the Ammonites in front, and by the Syrian auxiliaries behind, Joab resolved to attack the latter-the more numerous and formidable host-while he directed his brother Abishai, with a suitable detachment, to attack the Ammonites. Joab's address before the engagement displays the faith and piety that became a commander of the Hebrew people. The mercenaries being defeated, the courage of the Ammonites failed, so that, taking flight, they entrenched themselves within the fortified walls.