The early history of the site is unknown, although the site was almost certainly settled many years before the medieval castle was built. Although Roman remains are few, there is ample evidence of Anglo Saxon settlement in the area. Windsor Castle was originally built by William the Conqueror in the decade after the Norman conquest of 1066.
The town of New Windsor, as an ancient demesne of the Crown, was a privileged settlement, Windsor was granted royal borough status by Edward I's charter in 1277.
New Windsor was a nationally significant town in the Middle Ages. Its prosperity came from its close association with the royal household. The development of the castle under Edward III, was the largest secular building project in England of the Middle Ages. Henry III, a hundred years earlier, had spent more on Windsor Castle than on any other royal building project, save the rebuilding of Westminster Abbey.
Windsor became a major pilgrimage destination, particularly for Londoners. Pilgrims came to touch the royal shrine of the murdered Henry VI and the fragment of the True Cross. Windsor was the home of the New Model Army and the castle was garrisoned by Colonel Venn during the English Civil War.