The fighting continued for three hours, according to research by English Heritage, a government body in charge of conservation of historic sites. It was indecisive until the arrival of Norfolk's men. Marching up the Old London Road, Norfolk's contingent was hidden from view until they crested the ridge and attacked the Lancastrian left flank. The Lancastrians continued to give fight but the advantage had shifted to the Yorkists. By the end of the day, the Lancastrian line had broken up, as small groups of men began fleeing for their lives. Polydore Vergil, chronicler for Henry VII of England, claimed that combat lasted for a total of 10 hours.