The keep (also known as a donjon) is the core structure of most medieval castles (although some later designs more or less eliminated them) and consists of a large, heavily fortified building around which the remainder of the fortifications are arranged. Depending on the overall plan of the castle, the keep may form part of the exterior walls or may be buried behind several curtains. Generally the keep will be taller than the curtain walls and should give the garrison as good a field of fire as possible against the rest of the castle. Traditionally a keep is entered on the first floor with the ground floor being heavily reinforced and any interior space used for storage.
Primarily the keep serves as a final redoubt, and so should be adequately supplied with food, water and storage for weapons and ammunition. Frequently this ends up implying that a significant portion of the castle's accomodation ends up being within the keep as well - this can lead to a very large and impressive - not to say expensive - structure that is pretty much a castle in its own right1. The alternative to the large, permanently inhabited keep is the bergfried design, where the "final redoubt" function is taken up by a tower designed solely for that purpose and most of the day to day life of the place goes on in less impressive structures built in the castle's various baileys. It is entirely possible for larger and older castles to have multiple keeps (or keep like structures) reflecting various phases of expansion and the lord of the castle may live within a keep or may choose to settle in a more comfortable structure at ground level.
Game and Story Use
- In any suitably dramatic siege, the defenders fall back wall by wall into the keep - combat may then move into the keep, room by room until the place is taken or relieved. This can very easily be complicated by multiple keeps in mutually supporting positions, especially if they happen to be linked by tunnels.
- In most cases the castle keep will be where PCs visit the lord of the castle to receive orders and rewards or to attend feasts, feudal courts and the like. As noted, this may not always be the case.
- Keeps - and more generally castles - that will play an important part in the campaign are usually worth mapping. Time travelling or very long lived PCs may be able to watch the place evolve over the years.