Pygmy Painted in Pompei Pokes a Hippo
"African Pygmies battle a hippopotamos on the river Nile: one spearing its back, whilst another is swallowed from a boat. Other Pygmies rein in a crocodile, as one rides its back." Fresco from 1st century AD, Pompeii Imperial Rome. - source.
Browse the galleries at the Theoi Greek Mythology website to see a good selection of Greek and Roman art.
The site also has a great beastiary.