The Erechtheum, or Erechtheion, is an ancient Greek temple on the north side of the Acropolis of Athens in Greece, notable for a design that is both elegant and unusual.

The temple as seen today was built between 421 BCE and 407 BCE. Its architect may have been Mnesicles, and it derived its name from a shrine dedicated to the legendary Greek hero Erichthonius. Some have suggested that it may have been built in honour of the legendary king Erechtheus, who is said to have been buried nearby. It is believed to have been a replacement for an older temple destroyed by the Persians around 480 BCE.

The temple itself was dedicated to Athena and Poseidon Erechtheus. Within the foundations lived the sacred snake of the temple, which represented the spirit of Cecrops and whose well-being was thought essential for the safety of the city. The snake was fed honey-cakes by Canephorae, the priestesses of Athena Polias, by custom the women of the ancient family of the Eteoboutadae. The snake's occasional refusal to eat the cakes was thought a disastrous omen.