The Erechtheion is an intricate temple. It sprang from a complex plan that was designed to accommodate the radically uneven ground on the site, and to avoid disturbing sacred shrines like the altars to Poseidon (Erechtheus), and Hephaestus, or the spot where Poseidon hit the Acropolis with his trident. Other shrines that needed to be accommodated included the sacred olive tree, a well containing sea water (the Erechtheian Sea), the tomb of Kekrops, and the Pandrosion sanctuary.