Early Norman castles were built from wood, but it seems that at Windsor, because the base of the mound was so strong, a stone castle was used early in its development. The castle that William built consisted of a wooden shell keep built around the mound, and two baileys, one to the east of the mound, and one to the west. Arundel is an example of another castle that has two baileys. The western bailey at Windsor is lower than the eastern one.
Henry I made improvements to Windsor Castle so that it could be used for the first time as a royal residence. He held court there in 1110 and married his second wife Adeliza of Louvain in its chapel. During his reign the wooden keep on the motte was replaced by stone. Between 1173 and 1179 Henry II spent time and money improving the keep again. The height of the keep was raised and the walls around the baileys were rebuilt.
During the reign of John, the castle was besieged twice, first in around 1193 when a minor siege occurred. In 1216 Prince Louis and a French army invaded the south of England. The French had been invited to England by rebels who were opposing King John's rule and were needed to help overthrow the King. Windsor castle along with Dover and Lincoln held out against the French, but Windsor was left badly damaged by the attack. After John died his son Henry III became king of England. Henry repaired the damage that had been inflicted during his father's reign.
Edward III is famous for making Windsor Castle the home of the Order of the Garter and the Round Table. This order of knights was created in 1344 based on the legendary stories of King Arthur and revolved around great feasts and tournaments. A huge wooden circular building was constructed in the eastern bailey to celebrate the Order's creation. After the death of Edward in 1377 the castle remained unchanged for almost a hundred years.
In 1400 the castle again came under attack. This time from the enemies of King Henry IV. Henry had deposed Richard II and not everyone was happy with this. The attackers managed to enter the castle through a postern gate in January of 1400 while the King celebrated Christmas. But the King had been warned of the attack and escaped to London. The rebels were caught a few days later and killed.