APHIDNA or APHIDNAE(Ἄφιδνα, Ἀφίδναι: Eth. Ἀφιδναῖος), one of the twelve ancient towns of Attica (Strab. 9. p. 397), is celebrated in the mythical period as the place where Theseus deposited Helen, entrusting her to the care of his friend Aphidnus. When the Dioscuri invaded Attica in search of their sister, the inhabitants of Deceleia informed the Lacedaemonians where Helen was concealed, and showed them the way to Aphidna. The Dioscuri thereupon took the town, and carried off their sister. (Hdt. 9.73; Diod. 4.63; Plut. Thes. 32; Paus. 1.17.5, 41.3.) We learn, from a decree quoted by Demosthenes ( de Coron. p. 238), that Aphidna was, in his time, a fortified town, and at a greater distance than 120 stadia from Athens. As an Attic demus, it belonged in succession to the tribes Aeantis (Plut. Quaest. Symp. 1.10; Harpocrat. s. v. Θυργωνίδαι), Leontis (Steph. B.; Harpocrat. l. c.), Ptolemais (Hesych.), and Hadrianis (Böckh, Corp. Inscr. 275).
Leake, following Finlay, places Aphidna between Deceleia and Rhamnus, in the upper valley of the river Marathon, and supposes it to have stood on a strong and conspicuous height named Kotróni, upon which are considerable remains indicating the site of a fortified demus. Its distance from Athens is about 16 miles, half as much from Marathon, and something less from Deceleia. (Leake, Demi of Attica, p. 19, seq.)