The Halos was a round open space close to the temple of Apollo in Delphi, where ancient rituals were being performed.
Between the Bouleuterion and Sibyl's Rock in the sanctuary of Apollo in Delphi there is a narrow pass leading to the fountain which the dragon Python was supposedly guarding.
Apollo killed the dragon and then left for the land of the Hyperboreans in order to be expiated from the murder.
At that spot, in front of the rocks marking the pass, a round square is formed, called Halos (literally: a threshing floor), where several rituals were taking place.
These ex votos had been destroyed at a prior phase, by fire or other causes, and, according to the practice in those days, they were buried because it was forbidden to recycle or sell them.