"an ensign at the Battle of Tannieres"
John Churchill, 1st Duke of Marlborough
Public DomainJohn Churchill, 1st Duke of Marlborough - Credit: Sir Godfrey Kneller

Historians suggest that Fielding is in fact referring to the Battle of Ramillies, which took place on 23 May 1706, and was a major engagement of the War of the Spanish Succession.  It saw the Grand Alliance (Austria, England, and the Dutch Republic) engaging the Bourbon armies of King Louis XIV.  Louis had urged his armies to go on the offensive in the Spanish Netherlands.  The French army of 60,000 encountered the Duke of Marlborough’s Anglo-Dutch force of 62,000 close to the small village of Ramillies.  In less than four hours Marlborough's forces overwhelmed the French.  The battle proved decisive, and a succession of towns soon fell to the Allies.  By the end of the campaign the French army had been driven from most of the Spanish Netherlands.