The largest compartment of the temple is the east cella (the inner chamber) with the Ionic portico on the east end. This part of the temple was accessible from the north side with a large staircase (much larger than the one currently in use). The temple was built entirely of marble from Mount Pentelikon (as was the Parthenon) but the friezes were made of black limestone and bore sculptures in white marble. The cella was accessible through a main door, while on either side of it there were narrow windows. Columns divided the interior into three aisles, while the sacred snake of Athena resided in a subterranean room beneath the marble floor.