What is "bergfried"

A bergfried (plural: bergfrieds or bergfriede) is a tall tower typically found in castles of the Middle Ages in German-speaking countries and in countries under German influence. Friar describes it as a "free-standing, fighting-tower". Its defensive function is to some extent similar to that of a keep (also known as a donjon) in English or French castles. However, the characteristic difference between a bergfried and a keep lies in the fact that a bergfried was typically not designed for permanent habitation.