One of the three daughter of Cecrops, being the other two Pandrosus and Herse.
A basket containing a marvelous child, Erichthonius, was given by the Goddess Athena into the care of the three daughters of Cecrops. The child was produced by the encounter between Athena and Hephaestus. The girls were told to guard the basket without looking into it. Aglaurus and Herse, went mad and perished, Pandrosus was the only one of the sisters to be faithful to the trust.
Aglaurus(and Herse?) had a Sanctuary in a cave at the north slope of the Acropolis at Athens. It was the place where Aglaurus supposedly had jumped to, out of insanity at having glimpsed the forbidden content of the basket. Herse shared the wrongdoing and the punishment with her.
Pausanias reports: It was to Aglaurus and her sisters, Herse and Pandrosus, that they say Athena gave Erichthonius, whom She had hidden in a chest, forbidding them to pry curiously into what was entrusted to their charge. Pandrosus, they say, obeyed, but the other two (for they opened the chest) went mad when they saw Erichthonius, and threw themselves down the steepest part of the Acropolis. (Paus. 1.18.2)
The death of Aglaurus was commemorated at the festival of the Plinteria and the Palladium of Athena Polias in the Erechtheum was veiled in sign of mourning (Paus. 8.46.2).