A patronymic from Heracles, and consequently given to all the sons and descendants of the Greek Heracles; but the name is also applied in a narrower sense to those descendants of the hero who, in conjunction with the Dorians, invaded and took possession of Peloponnesus.
The many sons of Heracles are enumerated by Apollodorus (ii. 7. § 8), though his list is very far from being complete; and a large number of tribes or noble families of Greece traced their origin to Heracles. In some of them the belief in their descent from Heracles seems to have arisen only from the fact, that the hero was worshipped by a particular tribe. The principal sons and descendants of Heracles are treated of in separate articles, and we shall here confine ourselves to those Heracleidae whose conquest of Peloponnesus forms the transition from mythology to history. It was the will of Zeus that Heracles should rule over the country of the Perseids, at Mycenae and Tiryns. Through Hera's cunning, however, Eurystheus had been put into the place of Heracles, and the latter had become the servant of the former. After the death of the two, the claims of Heracles devolved upon the sons and descendants of Heracles. The leader of these Heracleidae was Hyllus, the eldest of the four sons of Heracles by Deianeira. The descendants of Heracles, who, according to the tradition of the Dorians (Herod. v. 72), were in reality Achaeans, ruled over Dorians, as Heracles had received for himself and his descendants one third of the dominions of the Doric king, Aegimius, for the assistance he had given him against the Lapithae. The countries to which the Heracleidae had especial claims were Argos, Lacedaemon, and the Messenian Pylos, which Heracles himself had subdued : Elis, the kingdom of Augeas, might likewise be said to have belonged to him. (Apollod. ii. 7. § 2, &c.; Paus. ii. 18. § 6, &c., v. 3. § 1, &c.) The Heracleidae, in conjunction with the Dorians, invaded Peloponnesus, to take possession of those countries and rights which their ancestor had duly acquired. This expedition is called the return of the Heracleidae, kathodos tôn Hêrakleidôn. (Comp. Thuc. i. 12; Isocrat. Archid. 6.) They did not, however, succeed in their first attempt; but the legend mentions five different expeditions, of which we have the following accounts. According to some, it happened that, after the demise of Heracles, his son, Hyllus, with his brothers and a band of Arcadians, was staying with Ceyx at Trachis. As Eurystheus demanded their surrender, and Ceyx was unable to protect them, they fled to various parts of Greece, until they were received as suppliants at Athens, at the altar of Eleos, Mercy, (Apollod. ii. 8. § 1; Diod. iv. 57; Paus. i. 32. § 5; Longin. 27). According to the Heracleidae of Euripides, the sons of Heracles were at first staying at Argos, and thence went to Trachis, Thessaly, and at length to Athens. (Comp. Anton. Lib. 33.) Demophon, the son of Theseus, received them, and they settled in the Attic tetrapolis. Eurystheus, to whom the Athenians refused to surrender the fugitives, now made war on the Athenians with a large army, but was defeated by the Athenians under Iolaus, Theseus, and Hyllus, and was slain with his sons. Hyllus took his head to his grandmother, Alcmene; and the Athenians of later times showed the tomb of Eurystheus in front of the temple of the Pallenian Athena. The battle itself was very celebrated in the Attic stories as the battle of the Scironian rock, on the court of the Saronic gulf (comp Dem. de Coron. § 147), though Pindar places it in the neighbourhood of Thebes. (Pyth. ix. 137; comp. Anton. Lib. l. c; Herod. ix. 27; Eurip. Heracl.) After the battle, the Heracleidae entered Peloponnesus, and maintained themselves there for one year. But a plague, which spread over the whole peninsula, compelled them (with the exception of Tlepolemus, who went to Rhodes) to return to Attica, where, for a time, they again settled in the Attic tetrapolis. From thence, however, they proceeded to Aegimius, king of the Dorians, about the river Peneius, to seek protection. (Apollod. ii. 8. § 2; Strab. ix. p. 427.) Diodorus (iv. 57) does not mention this second stay in Attica, and he represents only the descendants of Hyllus as living among the Dorians in the country assigned to Heracles by Aegimius: others again do not notice this first expedition into Peloponnesus (Pherecyd. ap. Anton. Lib. l. c.), and state that Hyllus, after the defeat of Eurystheus, went with the other Heracleidae to Thebes, and settled there at the Electrian gate. The tradition then goes on to say that Aegimius adopted Hyllus, who, after the lapse of three years, in conjunction with a band of Dorians, undertook an expedition against Atreus, who, having married a daughter of Eurystheus, had become king of Mycenae and Tiryns. They marched across the Corinthian isthmus, and first met Echemus of Tegea, who fought for the interest of the Pelopidae, the principal opponents of the Heracleidae. Hyllus fell in single combat with Echemus, and according to an agreement which the two had entered into, the Heracleidae were not to make any further attempt upon the peninsula within the next fifty years. They accordingly went to Tricorythus, where they were allowed by the Athenians to take up their abode. During the period which now followed (ten years after the death of Hyllus), the Trojan war took place; and thirty years after the Trojan war Cleodaeus, son of Hyllus, again invaded Peloponnesus; and about twenty years later Aristomachus, the son of Cleodaeus, undertook the fourth expedition. But both heroes fell. Not quite thirty years after Aristomachus (that is, about 80 years after the destruction of Troy), the Heracleidae prepared for a great and final attack. Temenus, Cresphontes, and Aristodemus, the sons of Aristomachus, after having received the advice of an oracle, built a fleet on the Corinthian gulf; but this fleet was destroyed, because Hippotes, one of the Heracleidae, had killed Carnus, an Acarnanian soothsayer; and Aristodemus was killed by a flash of lightning. (Apollod. ii. 8. § 2; Paus. iii. 1. § 5.) An oracle now ordered them to take a three-eyed man for their commander. He was found in the person of Oxylus, the son of Andraemon. The expedition now successfully sailed from Naupactus towards Rhion in Peloponnesus. (Paus. viii. 5. § 4). Oxylus, keeping the invaders away from his own kingdom of Elis, led them through Arcadia. Cresphontes is said to have married the daughter of the Arcadian king, Cypselus, and Polycaon Euaechme, the daughter of Hyllus. Thebans, Trachinians, and Tyrrhenians, are further said to have supported the Heracleidae and Dorians. (Paus. iv. 3. § 4, viii. 5. § 4; Schol. ad Soph. Aj. 17; Eurip. Phoen. 1386; Pind. Pyth. v. 101, Isthm. vii. 18.) Being thus strongly supported in various ways, the Heracleidae and Dorians conquered Tisamenus, the son of Orestes, who ruled over Argos. Mycenae, and Sparta. (Apollod. l. c.; Paus. v. 3; Polyaen. i. 9.) The conquerors now succeeded without difficulty, for many of the inhabitants of Peloponnesus spontaneously opened their gates to them, and other places were delivered up to them by treachery. (Paus. ii. 4. § 3, iii. 13. § 2, iv. 3. § 3, v. 4. § 1; Strab. viii. p. 365.) They then distributed the newly acquired possessions among themselves by lot: Temenus obtained Argos; Procles and Eurystheus, the twin sons of Aristodemus, Lacedaemon; and Cresphontes, Messenia.