The simplest thing to build is a stronghold – a simple house strengthened to protect it from attackers. If this building stands on its own it is called a tower house.

It needs to have thick walls so it cannot be battered down. It should not have an entrance at ground level, for that would make it too easy to enter. It should only have slits for windows so that people inside could not be shot. It should have a lead roof so that fire arrows do no harm.

The tower is harder to attack if it is on a mound (called a motte) and surrounded by a ditch called a moat (if filled with water, it is even more effective).

The keep to a castle was nearly always placed on a motte. It was also far bigger than a tower house. You could think of it more like a block of apartments.

Keeps come in all shapes and sizes, depending on the choices of the designer at the time. The earliest British keeps were square, but the later ones were often round.

The keep sometimes had towers at the corners, which rose above the main building to act as watchtowers. The lowest floor was used as a store room. It was below ground level. In later years this part was used as a dungeon (prison).

The outside stairs were separated from the keep by a drawbridge. The first floor was used by the castle garrison. The second floor contained the main hall.

Sometimes there was an extra floor added for the lord or king's private apartments. This 'en-suite' room was known as a solar (from the French 'seulement', to be alone). This floor might also have a chapel.