Archaeological Museum of Eretria:
Terracotta figurine of a centaur (950-900 B.C), from the cemetery at Leukanti.
This is the earliest known representation of the mythical creature. It was found broken in two pieces with each individual piece at a different tomb, an indication that it was shared between two owners.
There is some discussion if the symbols painted on horse figures were also painted on actual horses. To me it also seems as if he is wearing a harness of some sort.