A castle (from Latin castellum) is a type of fortified structure built in Europe and the Middle East during the Middle Ages by nobility. A castle is usually the private fortified residence of a lord or noble. A keep (from the Middle English kype) is a type of fortified tower built within castles during the Middle Ages by European nobility. It refers to large towers in castles that were fortified residences. Although often the strongest part of a castle and a last place of refuge if the outer defences fell, the keep was not left empty in case of attack but was used as a residence by the lord who owned the castle, or his guests or representatives. Keep was not a term used in the medieval period – the term was applied from the 16th century onwards – instead the French 'donjon' was used to refer to great towers. In motte-and-bailey castles, the keep was on top of the motte. In Italian the keep is called 'mastio'; in Germany the use of tall towers called 'bergfried', rather than keeps in the western fashion, were preferred. However, the characteristic difference between a bergfried, a mastio, and a keep lies in the fact that both the bergfried and the mastio were typically not designed for permanent habitation, but for military use, though they could be inhabited in case of need. Thanks for your kind comments.