Colchester Castle is a Norman castle in Colchester, Essex, England, dating from the second half of the eleventh century. The keep of the castle is mostly intact and is the largest example of its kind anywhere in Europe, due to its being built on the foundations of the Roman Temple of Claudius, Colchester.

The Colchester Castle keep in Essex, England, holds the title of the largest Norman keep ever built in Europe. Constructed starting in 1076 on the massive stone foundations of the Roman Temple of Claudius, it measures approximately 46 meters by 33.5 meters (151 by 110 feet). Its sheer size was necessitated by the need to fortify the newly conquered English territory and to reuse the existing Roman footprint. Interestingly, while it is the largest by area, it is not the tallest; it was likely intended to be higher but was kept lower for defensive stability. It is even larger than the famous White Tower at the Tower of London, which was built around the same time. Today, the castle serves as an award-winning museum, showcasing Roman and Norman history. Another strong contender often mentioned is the Château de Vincennes near Paris, which features the tallest medieval fortified keep in Europe (52 meters), but in terms of the total ground footprint and massive volume of a "great keep," Colchester remains the undisputed champion.