Herstmonceux Castle was built on the site of former house by Roger de Fiennes who received a licence to crenellate in 1441.
As Treasurer of the Household to Henry VI he built a splendid fortified mansion in keeping with the status of his high office.
The castle was built in a lake and constructed of Flemish brick.
The gatehouse has two imposing towers rising to 84 feet on either side of the entrance and a draw bridge. Each of the octagonal and semi- octagonal towers had defences suitable for firearm or cross bow but the walls were too thin to withstand any artillery bombardment. However the castle saw little military action.
The main threat to the castle was neglectful owners and in the 1770's the Rev. Robert Hare used bricks from the castle to build a new house.
The castle remained as a ruin until Sir Claude Lowther began to restore the castle using the original plans.
The work was completed by Sir Paul Latham.
Herstmonceux Castle housed the Royal Observatory from 1949 to 1989 and today it is used a conference centre.
The castle is not open to the public except by tours, but the gardens and Science Centre are open.