<P> Windsor Castle's position on top of steep ground has meant that the castle's gardens are limited in scale . The castle gardens stretch east from the Upper Ward across a 19th - century terrace . Windsor Castle is surrounded by extensive parkland . The immediate area stretching to the east of the castle is a 19th - century creation known as the Home Park . The Home Park includes parkland and two working farms, along with many estate cottages mainly occupied by employees and the Frogmore estate . The Long Walk, a double lined avenue of trees, runs for 2.65 miles (4.26 km) south of the castle, and is 240 ft (75 m) wide . The original 17th - century elms were replaced with alternating chestnut and plane trees . The impact of Dutch elm disease led to large - scale replanting after 1945 . </P> <P> The Home Park adjoins the northern edge of the more extensive Windsor Great Park, occupying some 5,000 acres (2,020 ha) and including some of the oldest broadleaved woodlands in Europe . In the Home Park, to the north of the castle, stands a private school, St George's, which provides choristers to the chapel . Eton College is located about half a mile from the castle, across the River Thames, reflecting the fact that it was a royal foundation of Henry VI . </P> <P> Windsor Castle was originally built by William the Conqueror in the decade after the Norman conquest of 1066 . William established a defensive ring of motte and bailey castles around London; each was a day's march--about 20 miles (32 km)--from the city and from the next castle, allowing for easy reinforcements in a crisis . Windsor Castle, one of this ring of fortifications, was strategically important because of its proximity to both the River Thames, a key medieval route into London, and Windsor Forest, a royal hunting preserve previously used by the Saxon kings . The nearby settlement of Clivore, or Clewer, was an old Saxon residence . The initial wooden castle consisted of a keep on the top of a man - made motte, or mound, protected by a small bailey wall, occupying a chalk inlier, or bluff, rising 100 ft (30 m) above the river . A second wooden bailey was constructed to the east of the keep, forming the later Upper Ward . By the end of the century, another bailey had been constructed to the west, creating the basic shape of the modern castle . In design, Windsor most closely resembled Arundel Castle, another powerful early Norman fortification, but the double bailey design was also found at Rockingham and Alnwick Castle . </P> <P> Windsor was not initially used as a royal residence; the early Norman kings preferred to use the former palace of Edward the Confessor in the village of Old Windsor . The first king to use Windsor Castle as a residence was Henry I, who celebrated Whitsuntide at the castle in 1110 during a period of heightened insecurity . Henry's marriage to Adela, the daughter of Godfrey of Louvain, took place in the castle in 1121 . During this period the keep suffered a substantial collapse--archaeological evidence shows that the southern side of the motte subsided by over 6 ft (2 m). Timber piles were driven in to support the motte and the old wooden keep was replaced with a new stone shell keep, with a probable gateway to the north - east and a new stone well . A chemise, or low protective wall, was subsequently added to the keep . </P>

When was the royal castle in england built