Leaving some 6,000 men to continue the siege, Turenne advanced to meet the Spanish army. The battle on 14 June 1658 which resulted from this manoeuvre became known as the "Battle of the Dunes" because the Spanish army formed their line upon a line of dunes, or sand-hills, also called the Downs, perpendicular to the sea. Napoleon described the battle as Turenne's "... most brilliant action". The red-coats of the New Model Army under the leadership of Sir William Lockhart, Cromwell's ambassador at Paris in Turenne's army, astonished both armies by the stubborn fierceness of their assault up a sand-hill high and strongly defended by Spanish veterans.