The races themselves were held in the hippodrome, which held both chariot races and riding races. The single horse race was known as the "keles" ("keles", Greek: κέλης). The hippodrome was situated at the south-east corner of the sanctuary of Olympia, on the large flat area south of the stadium and ran almost parallel to the latter. Until recently, its exact location was unknown, since it is buried by several meters of sedimentary material from the Alfeios River. In 2008, however, Annie Muller and staff of the German Archeological Institute used radar to locate a large, rectangular structure similar to Pausanias's description. Pausanias, who visited Olympia in the second century AD, describes the monument as a large, elongated, flat space, approximately 780 meters long and 320 meters wide (four "stadia" long and one "stade" four "plethra" wide). The elongated racecourse was divided longitudinally into two tracks by a stone or wooden barrier, the "embolon". All the horses or chariots ran on one track toward the east, then turned around the "embolon" and headed back west. Distances varied according to the event. The racecourse was surrounded by natural (to the north) and artificial (to the south and east) banks for the spectators; a special place was reserved for the judges on the west side of the north bank.