Hagnus (Ancient Greek: Ἁγνοῦς, romanized: Hagnous) was a deme of ancient Attica. From the mythical story of the war of the Pallantidae against Theseus, we learn that the demoi of Pallene, Gargettus, and Agnus were adjacent. When Pallas was marching from Sphettus in the Mesogaea against Athens, he placed a body of his troops in ambush at Gargettus, under the command of his two sons, who were ordered, as soon as he was engaged with the army of Theseus, to march rapidly upon Athens and take the city by surprise, But the stratagem was revealed to Theseus by Leos of Agnus, the herald of Pallas; whereupon Theseus cut to pieces the troops at Gargettus. In consequence of this a lasting enmity followed between the inhabitants of Pallene and Agnus.
The road from Sphettus to Athens passed through the opening between Mount Pentelicus and Mount Hymettus. A monastery there by the name of Ieraka (or Hieraka) is the site of Gargettus. The proximity of Pallene and Gargettus is indicated by another legend. Pallene was celebrated for its temple of Athena; and we are told that Eurystheus was buried at Gargettus in front of the temple of Athena Pallenis. We know further that Pallene lay on one of the roads from the city to Marathon.
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