Now called the Old Temple of Athena, the remains of a temple stand immediately south of the Erecthion and its foundations are visible. The nature, age, and indeed, everything else about this building, are highly debated and little is truly known.

The Erecthion is one of the most unusual Greek temples, built upon several levels and incorporating various myths, gods, and previous sacred sites. Legend has it that Athena and Poseidon held a contest to see who would possess the Acropolis. Poseidon created a salt water spring, the Erectheis, by throwing down his trident and Athena created an olive tree. Athena was judged the winner and Poseidon, in anger, caused a flood. However, the two gods were reconciled and both were worshipped at the spot.

Another myth tells of the god Hephaestus, who attempted to rape Athena. Athena managed elude him at the last possible moment and Hephaestus accidentally impregnated the earth. Immediately, Erecthonius sprang up on the spot, a child with snake (earth) attributes. Athena took the child and eventually raised it. Erecthonius later became king of Athens and erected a statue to her on the Acropolis. At some time, for reasons unknown, Poseidon and Erecthonius became associated with each other. The cult here worshipped all three of them, along with the hero Boutes. Additionally, the cult honored the supposed olive tree of Athena, the trident marks of Poseidon, and the tomb of Cecrops.