Visions of St. Thomas Becket and St. George, both England's national saints, are said to have during the Battle of Lewes in 1264 in which Simon de Monfort defeats Henry III's royalist forces.
Battle of Lewes - Wikipedia
The Song of Lewes, p. 85
Magna Carta Project
Laura Ashe (2017). The Oxford English Literary History: Volume I: 1000-1350: Conquest and Transformation. OUP Oxford. pp. 368–. ISBN 978-0-19-253444-6.