A circular marble building — a tholos — that stands at the northwestern corner of the Altis, the sacred precinct of the sanctuary. It was commissioned by Philip II of Macedon, who wanted to mark his new dominance over the Greek world in the most visible religious space available. The structure had an outer ring of Ionic columns and an inner ring of Corinthian half-columns, an unusual combination that gave the interior a layered grandeur.
Today several columns have been restored upright and the round foundations are clearly visible. It is one of the best-preserved structures on the site and gives a good sense of Macedonian architectural ambition. Philip was assassinated before its completion; it was finished by Alexander.