This page contains information from two public domain works: the 1911 Encyclopedia Britannica and Easton's Bible Dictionary (1897). Refactoring, merging, NPOVing and updating required.
Ammonites, also referred to in the Bible as the "children of Ammon," were a people of eastern Palestine who along with the Moabites traced their origin to Lot, the nephew of the patriarch Abraham, and were regarded as close relatives of the Israelites and Edomites. Both the Ammonites and Moabites are sometimes spoken of under the common name of the children of Lot (Deuteronomy 2:19; Psalms 83:8). Both tribes hired Balaam to curse Israel, which he instead blessed (Deuteronomy 23:4). Also known as the Beni-ammi (Genesis 19:38), the Ammonites and the Israelites throughout the Old Testament and recorded history were antagonists.
When the Israelites on the Exodus paused before their territory, the Ammonites prohibited them from passing through their lands. For this act, they were denied entry into "the congregation of the Lord" until ten generations had passed (Deuteronomy 23:3). In the time of the judges, Jephthah waged war against them and took twenty of their cities (Judges 11:33). They they were defeated by Saul, the first king of united Israel (1 Samuel 11:11), and a generation later, along with the Syrians, by David (2 Samuel 10:6-14) who took their chief city Rabbah. David's son Solomon had an Ammonite wife, Naamah, who became the mother of Rehoboam (1 Kings 14:31; 2 Chronicles 12:13).
Traditionally, the original territory of the two tribes was the country lying immediately east of the Dead Sea and the lower half of the Jordan, with the Jabbok for its northern boundary; the Ammonites laid claim to the northern portion between the Arnon and the Jabbok, from which they had expelled the Zamzummim (Judges 11:13; Deuteronomy 2:20; cf. Genesis 14:5). From this original territory they had been expelled by Sihon, king of the Amorites, who was said to have been found by the Israelites, after their deliverance from Egypt, in possession of both Gilead and Bashan, that is, of the whole country on the left bank of the Jordan, lying to the north of the Arnon (Numbers 21:13). By this invasion, the Ammonites were driven out of Gilead across the upper waters of the Jabbok where it flows from south to north, which henceforth continued to be their western boundary (Numbers 21:24; Deuteronomy 2:37 and 3:16). The other limits of the Ammonitis, or country of the Ammonites ('Lmmanitis chora, 2 Maccabees 4:26) were not exactly defined. On the south it probably adjoined the land of Moab; on the north it may have met that of the king of Geshur (Joshua 12:5); and on the east it may have melted away into the desert peopled by Amalekites and other nomadic races.
The chief city of the country was Rabbah or Rabbath of the children of Ammon, i.e. the metropolis of the Ammonites (Deuteronomy 3:11), and Rabbathammana by the later Greeks (Polyb, v. 7. 4). Ptolemy Philadelphus changed its name to Philadelphia and made it a large and strong city with an acropolis and situated it on both sides of a branch of the Jabbok, today known as Nahr `Amman, the river of Ammon, whence the designation "city of waters" (2 Samuel 12:27); see Survey of E. Pal (Pal. Explor. Fund), pp. 19 sqq. The ruins called Amman by the natives are extensive and imposing. The country to the south and east of Amman is distinguished by its fertility; and ruined towns are scattered thickly over it, attesting that it was once occupied by a population which, however fierce, was settled and industrious, a fact indicated also by the tribute of corn paid annually to Jotham (2 Chronicles 27:5).
The traditional history of Ammon as related in the Old Testament is not free from obscurity, due to the uncertain dating of the various references. (See further MOAB.) From the Assyrian inscriptions we learn that the Ammonite king Ba'sa (Baasha) (son) of Ruhubi, with 1000 men joined Ahab and the Syrian allies against Shalmaneser II. at the Battle of Qarqar in 854. In 734 their king Sanip(b)u was a vassal of Tiglathpileser IV and his successor, P(b)udu-ilu, held the same position under Sennacherib and Esarhaddon. Somewhat later, their king Amminadab was among the tributaries who suffered in the course of the great Arabian campaign of Assurbanipal. With the neighbouring tribes, the Ammonites helped the Babylonian monarch Nebuchadrezzar against Jehoiakim (2 Kings 24:2); and if they joined Zedekiah's conspiracy (Jeremiah 27:3), and were threatened by the Babylonian army (Ezekiel 21:20), they do not appear to have suffered greatly.
After the destruction of Jerusalem, the fugitive Jews were again gathered together. At the instigation of the Ammonite king Baalis, Gedaliah, the ruler whom Nebuchadrezzar had appointed over them, was murdered, and new calamities were incurred (Jeremiah 40:14); and when Nehemiah prepared to rebuild the walls of Jerusalem an Ammonite was foremost in opposition (Nehemiah 2: 10, 19, iv. 1-3) True to their antecedents, the Ammonites, with some of the neighbouring tribes, did their utmost to resist and check the revival of the Jewish power under Judas Maccabaeus (1 Maccabees v. 6; cf. Jos. Ant. Jud. xii. 8. 1.). The last notice of the Ammonites themselves is in Justin Martyr (Dial. cum Tryph. sec. 119), where it is affirmed that they were still a numerous people. The few Ammonite names that have been preserved (Nahash, Hanun, and those mentioned above, Zelek in 2 Samuel 23:37 is textually uncertain) testify, in harmony with other considerations, that their language was Semitic, closely allied to the Hebrew language and the Moabite language Their national deity was Moloch or Milcon, at whose altar the Ammonites offered human sacrifices (2 Kings 23:13).