bergfried

They added a small residence in the 14th century and the donjon (also called a Bergfried or keep) developed as a stronghold of the Electoral archives and valuables.

Successive archbishops continued to improve the fortifications with stronger walls and expanded moats, adding levels to the central Bergfried, which was cylindrical, not square like many medieval donjons, expanded the inner works to include a small residence, dungeons, and chapel, fortified the walls, added a curtain wall, and improved the roads.

Bergfried, which take their name from the German for a belfry, were in one sense similar to keeps, but are usually distinguished from them on account of bergfied having a smaller area or footprint, usually being non-residential and being typically integrated into the outer defences of a castle, rather than being a safe refuge of last resort.