From BiblePortal Wikipedia

American Tract Society Bible Dictionary [1]

Or Rabbath-Ammon afterwards called Philadelphia, the capital of the Ammonites, was situated near the southern source of the jabbok, some twenty-two miles beyond Jordan. It was famous even in the time Moses,  Deuteronomy 3:11   Joshua 13:25 . When David declared war against the Ammonites, his general, Joab, laid siege to Rabbath-Ammon, where Uriah lost his life by a secret order of his prince; and when the city was reduced to the last extremity, Joab sent for David to hasten and go thither, to enjoy the honor of taking it,  2 Samuel 11:12 . From this time it became subject to the kings of Judah; but the kings of Israel subsequently became masters of it, with the tribes beyond Jordan. Towards the conclusion of the kingdom of Israel, Tiglathpileser having taken away a great part of the Israelites, the Ammonites were guilty of many cruelties against those who remained; for which the prophets Jeremiah and Ezekiel pronounced very severe prophecies against Rabbath, their captial, and against the rest of the country; which probably had their completion five years after the destruction of Jerusalem,  Jeremiah 49:1-3   Ezekiel 21:20 .

Antiochus the Great afterwards took the city. It was long known to the Greeks and Romans as Philadelphia; but this name is now unknown in that vicinity, while the more ancient name still survives. It is now called Amman, and is about fifteen miles southeast of Szalt, the ancient Ramoth-Gilead. Burckhardt found there extensive runs, which he has described. He and numerous other travellers found it desolate, as had been foretold; it was literally "a stable for camels," "a couching-place for flocks,"  Ezekiel 25:5 .

Holman Bible Dictionary [2]

 Deuteronomy 3:11 Ezekiel 21:20

Watson's Biblical & Theological Dictionary [3]

or RABBAT-AMMON, the capital city of the Ammonites, situated beyond Jordan. See Ammon .