The White Horse of Uffington.

The White Horse of Uffington, with its elegant lines of white chalk
bedrock, is thought to be the oldest hill figure in Britain. The image
is a stylised representation of a horse (some would say dragon) some
374 feet in length, and is thought to date back as far as 1000BC in the
late Bronze Age. Similar images have been found depicted on coins from
that period, and it is thought that the figure represents a horse
goddess connected with the local Belgae tribe. The goddess is generally
believed to be one form of Epona, worshiped throughout the Celtic world.

The horse was ritually scoured every seven years under the jurisdiction of the local Lord, who had to fund the event. The festival - for that is
what it became - could last for over three days and consisted of fun and games, traditional cheese rolling, wrestling and other pastimes. The focus of the games was in the enclosed earthen banks of Uffington Castle an Iron Age hill fort, which the White Horse seems to be galloping to when viewed from the air. The cheese rolling was held on the steep sided valley known as The Manger, the place where the horse was said to feed on moonlit nights. The festival, which may have had ancient origins, lapsed about a hundred years ago, and it is fortunate that the White Horse did not become completely overgrown. The horse isnow cleaned by members of English Heritage, who are responsible for the site.
--Mysterious Britain