History of Windsor Castle 
For over 900 years there has been a castle at Windsor. William the Conqueror chose the site, high above the River Thames and on the edge of a Saxon hunting ground. It was a day's march from the Tower of London and intended to guard the western approaches to the capital. Since those early days Windsor Castle has been inhabited continuously and improved upon by successive sovereigns. Some were great builders, strengthening the Castle against uprising and rebellion; others, living in more peaceful times, created a palatial royal residence.
Nine centuries after its foundation, the Castle continues to perform its prime role as one of The Queen's official residences. Pivotal to this role are the State Apartments, which are the formal rooms used for Court ceremonial and State and official occasions. They range from the smaller intimate rooms of Charles II's Apartments to the vast area of the Waterloo Chamber, built to commemorate the famous victory over Napoleon in 1815.