The temple rises from a stepped base or stylobate, which elevates the structure above the ground on which it stands. Early examples, such as the Temple of Zeus at Olympus, have two steps, but the majority, like the Parthenon, have three, with the exceptional example of the Temple of Apollo at Didyma having six. The core of the building is a masonry-built naos within which is a cella, a windowless room originally housing the statue of the god. The cella generally has a porch or pronaos before it, and perhaps a second chamber or antenaos serving as a treasury or repository for trophies and gifts. The chambers were lit by a single large doorway, fitted with a wrought iron grill. Some rooms appear to have been illuminated by skylights.