A metope....

Which, it seems, is an architectural panel to fit between two longer sections in a frieze. Lord Elgin, while Ambassador in Constantinople packed up and pinched/brought back great chunks of the Parthenon in Greece for "safe keeping".

Museums up and down Britain were quick to get casts made to share the aesthetic.

Here we have a Centaur and a Lapith in a struggle. The Centaurs (half men and half horses) and Lapiths were neighbours in Northern Greece. The Centaurs got invited to a Lapith wedding, and after a glass or two reverted to their usual randy selves. They tried to abduct the bride and all the women for their own purposes. It's a common them in Greek mythology and represents the struggle between civilisation and barbarism.

The fig leaf is not original, and is a 19th century addition! The Centaur is not similarly adapted - presumably because horse bits are all right.