E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
of Wantage (Berkshire), cut in the chalk hills. This horse commemorates a great victory gained by Alfred over the Danes, in the reign of his brother Ethelred I. The battle is called the battle of Æscesdun (Ashtree-hill). The horse is 374 feet long, and may be seen at the distance of fifteen miles. (Dr. Wise.)
An annual ceremony was once held, called Scouring the White Horse.