New Revised Standard Version
Now Joab fought against Rabbah of the Ammonites, and took the royal city.

Contemporary English Version
Meanwhile, Joab had been in the country of Ammon, attacking the city of Rabbah. He captured the royal fortress

New American Bible
Joab fought against Rabbah of the Ammonites and captured that royal city.

Douay-Rheims Bible
And Joab fought against Rabbath of the children of Ammon, and laid close siege to the royal city.

And Joab fought against Rabbath of the children of Ammon, and laid close siege to the royal city.

Joab

2 Samuel 11:25 And David said to the messenger: Thus shalt thou say to Joab: Let not this thing discourage thee: for various is the event of war: and sometimes one, sometimes another is consumed by the sword: encourage thy warriors against the city, and exhort them that thou mayest overthrow it.

1 Chronicles 20:1 And it came to pass after the course of a year, at the time that kings go out to battle, Joab gathered together an army and the strength of the troops, and wasted the land of the children of Ammon: and went and besieged Rabba. But David stayed at Jerusalem, when Joab smote Rabba, and destroyed it.

Rabbah.

19 miles to the S.E. by E. of Szalt, and lies along the banks of a river called Moiet Amman, which has its source in a pond, at a few hundred paces from the south-western end of the town, and empties itself in the Zerka, or Jabbok, about four hours to the northward. This river runs in a valley bordered on both sides by barren hills of flint, which advance on the south side close to the edge of the stream. The edifices which still remain, though in a decaying state, from being built of a calcareous stone of moderate hardness, sufficiently attest the former greatness and splendour of this metropolis of the children of Ammon.