Originally an Aethiopian or Libyan divinity, whose worship subsequently spread all over Egypt, a part of the northern coast of Africa, and many parts of Greece. The real Egyptian name was Amun or Ammun (Herod. ii. 42; Plut. de Is. et Os. 9); the Greeks called him Zeus Ammon, the Romans Jupiter Ammon, and the Hebrews Amon. (Jerem. xlvi. 25.) That in the countries where his worship was first established he was revered in certain respects as the supreme divinity, is clear from the fact, that the Greeks recognised in him their own Zeus, although the identity of the two gods in later times rests upon philosophical speculations, made at a period when the original character of Ammon was almost lost sight of, and a more spiritual view of him substituted in its place.
The most ancient seat of his worship appears to have been Meroe, where he had a much revered oracle (Herod. ii. 29); thence it was introduced into Egypt, where the worship took the firmest root at Thebes in Upper Egypt, which was therefore frequently called by the Greeks Diospolis, or the city of Zeus. (Herod. ii. 42; Diod. i. 15.) Another famous seat of the god, with a celebrated oracle, was in the oasis of Ammonium (Siwah) in the Libyan desert; the worship was also established in Cyrenaica. (Paus. x. 13. § 3.) The god was represented either in the form of a ram, or as a human being with the head of a ram (Herod. l. c. ; Strab. xvii. p. 812); but there are some representations in which he appears altogether as a human being with only the horns of a ram. Tertullian (de Pall. 3) calls him dives ovium. If we take all these circumstances into consideration, it seems clear that the original idea of Ammon was that of a protector and leader of the flocks. The Aethiopians were a nomadic people, flocks of sheep constituted their principal wealth, and it is perfectly in accordance with the notions of the Aethiopians as well as Egyptians to worship the animal which is the leader and protector of the flock. This view is supported by various stories about Ammon. Hyginus (Poet. Astr. i. 20) whose account is only a rationalistic interpretation of the origin of the god's worship, relates that some African of the name of Ammon brought to Liber [Dionysus], who was then in possession of Egypt, a large quantity of cattle In return for this, Liber gave him a piece of land near Thebes, and in commemoration of the benefits he had conferred upon the god, he was represented as a human being with horns. What Pausanias (iv.23. § 5) and Eustathius (ad Dionys. Perieg. 212) remark, as well as one of the many etymologies of the name of Ammon from the Egyptian word Amoni, which signifies a shepherd, or to feed, likewise accord with the opinion that Ammon was originally the leader and protector of flocks. Herodotus relates a story to account for the ram's head (ii. 42) : Heracles wanted to see Zeus, but the latter wished to avoid the interview; when, however, Heracles at last had recourse to entreaties, Zeus contrived the following expedient : he cut off the head of a ram, and holding this before his own head, and having covered the remaining part of his body with the skin of the ram, he appeared before Heracles. Hence, Herodotus adds, the Thebans never sacrifice rams except once a year, and on this one occasion they kill and flay a ram, and with its skin they dress the statue of Zeus (Ammon); by the side of this statue they then place that of Heracles. A similar account mentioned by Servius (ad Aen. iv. 196) may serve as a commentary upon Herodotus. When Bacchus, or according to others, Heracles, went to India and led his army through the deserts of Libya, he was at last quite exhausted with thirst, and invoked his father, Jupiter. Hereupon a ram appeared, which led Heracles to a place where it opened a spring in the sand by scraping with its foot. For this reason, says Servius, Jupiter Ammon, whose name is derived from ammos (sand), is represented with the horns of a ram. (Comp. Hygin. Fab. 133, Poet. Astr. i. 20 ; Lucan, Pharsal. ix. 511.) There are several other traditions, with various modifications arising from the time and place of their origin; but all agree in representing the ram as the guide and deliverer of the wandering herds or herdsmen in the deserts, either in a direct way, or by giving oracles. Ammon, therefore, who is identical with the ram, is the guide and protector of man and of all his possessions ; he stands in the same relation to mankind as the common ram to his flock.
The introduction of the worship of Ammon from Aethiopia into Egypt was symbolically represented in a ceremony which was performed at Thebes once in every year. On a certain day, the image of the god was carried across the river Nile into Libya, and after some days it was brought back, as if the god had arrived from Aethiopia. (Diod. i. 97.) The same account is given by Eustathius (ad Hom. Il. v. p. 128), though in a somewhat different form ; for he relates, that according to some, the Aethiopians used to fetch the images of Zeus and other gods from the great temple of Zeus at Thebes. With these images they went about, at a certain period, in Libya, celebrated a splendid festival for twelve days -- for this, he adds, is the number of the gods they worship. This number twelve contains an allusion to the number of signs in the zodiac, of which the ram (caper) is one. Thus we arrive at the second phasis in the character of Ammon, who is here conceived as the sun in the sign of Caper. (Zeus disguised in the skin of a ram. See Hygin. Fab. 133, Poet. Astr. i. 20; Macrob. Sat. i. 21. 18; Aelian, V. H. x. 18.) This astronomical character of Ammon is of later origin, and perhaps not older than the sixth century before Christ. The speculating Greeks of still later times assigned to Ammon a more spiritual nature. Thus Diodorus, though in a passage (iii. 68, &c.) he makes Ammon a king of Libya, describes him (i. 11, &c.) as the spirit pervading the universe, and as the author of all life in nature. (Comp. Pint. de Is. et Os. 9, 21.) The new Platonists perceived in Ammon their demiurgos, that is, the creator and preserver of the world. As this subject belongs more especially to the mythology of Egypt, we cannot here enter into a detailed discussion about the nature and character which the later Greeks assigned to him, or his connexion with Dionysus and Heracles. Respecting these points and the various opinions of modern critics, as well as the different representations of Ammon still extant, the reader may consult Jablonsky, Pantheon Aegypt.; Bohlen, Das alte Indien, mit besonderer Rücksicht auf Egypten, ii. c. 2. § 9; J. C. Prichard, Egyptian Mythology ; J. F. Champollion, Panthéon Egyptien, ou Collection des Personages de l'ancienne Egypte, &c., Paris, 1823.
The worship of Ammon was introduced into Greece at an early period, probably through the medium of the Greek colony in Cyrene, which must have formed a connexion with the great oracle of Ammon in the Oasis soon after its establishment. Ammnon had a temple and a statue, the gift of Pindar, at Thebes (Paus. ix. 16. § 1), and another at Sparta, the inhabitants of which, as Pausanias (iii. 18. § 2) says, consulted the oracle of Ammon in Libya from early times more than the other Greeks. At Aphytis, Ammon was worshipped, from the time of Lysander, as zealously as in Ammonium. Pindar the poet honoured the god with a hymn. At Megalopolis the god was represented with the head of a ram (Paus. viii. 32. § 1), and the Greeks of Cyrenaica dedicated at Delphi a chariot with a statue of Ammmon. (x. 13. § 3.) The homage which Alexander paid to the god in the Oasis is well known.