The impressive edifice (12.5m × 8.30 m) has the form of a temple, probably dating back to the late 5th century B.C .It was made of massive limestone and its interior was divided in two connected chambers. The eastern chamber was 3.15 meters long, had the form of a pronaos (vestibule) and was ornate with columns. Until today, the use of the edifice has not been verified.
It is believed to be a cenotaph, while many researchers share the opinion that it is the temple of Karneios Apollo. Although there is no indication on the correlation between the temple and the legendary king of Sparta, according to local tradition and the travel writer Pausanias, the remains of Leonidas were transferred and buried there. It is because of this, that the locals believe it to be the tomb of Leonidas. Pausanias also mentions that annual games were hosted here to honor the memory of the Spartan king.