Cylon (also spelled Kylon) was an Athenian associated with the first reliably dated event in Athenian history, the Cylonian affair.
Cylon, one of the Athenian nobles and a previous victor of the Olympic Games, attempted a coup in 632 BC with support from Megara, where his father-in-law Theagenes was tyrant. The oracle at Delphi had advised him to seize Athens during a festival of Zeus, which Cylon understood to mean the Olympics. However, the coup was opposed, and Cylon and his supporters took refuge in Athena's temple on the Acropolis. Cylon and his brother escaped, but his followers were cornered by Athens's nine archons. According to Plutarch and Thucydides (1.126), they were persuaded by the archons to leave the temple and stand trial after being assured that their lives would be spared.
In an effort to ensure their safety, the accused tied a rope to the temple's statue and went to the trial. On the way the rope (again, according to Plutarch) broke of its own accord. The Athenian archons, led by Megacles, took this as the goddess's repudiation of her suppliants and proceeded to stone them to death (on the other hand, Herodotus, 5.71, and Thucydides, 1.126, do not mention this aspect of the story, stating that Cylon was simply killed after being convinced that he would not be harmed).
Megacles and his genos, the Alcmaeonidae, were then exiled from the city for violating the laws against killing suppliants. The Alcmaeonidae were cursed with a miasma ("stain" or "pollution"), which was inherited by later generations, even after the genos retook control of Athens.