During the Battle of Evesham in 1265, the English royalists wore a red cross on a white uniform to identify themselves as being separate from the rebel barons that had worn white crosses during the Battle of Lewes just some months before. Ten years later, the St George’s Cross was used as England’s identifying emblem during the Welsh War.
Some historians believe that the St George’s Cross was adopted from Genoa’s flag in 1190 for use on English sailing vessels that were going into the Mediterranean and Black seas so that the Genoese fleets would protect them.
The flag of the United Kingdom (also known as the Union Jack) has incorporated the St George’s Cross from the English flag to a major degree. The St Patrick’s Cross (a red “x” on a white background) has also been used to indicate the merger of the Kingdom of Great Britain with the Kingdom of Ireland. This flag continues to be used to represent the United Kingdom, despite the fact that only Northern Ireland remains a member of the union.