In the Middle Ages, doors were locked via a latch on the interior, which was worked by a handle on the exterior.
This method was replaced around the 15th Century by the lock known as "staple plate lock", which was made up of a horizontal sliding bolt, operated by two flat ballotiere knobs on the interior and exterior. This horizontal bolt is immobilised by a vertical bolt operated by key from the exterior.

At this time, it was also customary to fit locks to chests. These would be made of thin plates of iron, carved in the style of the day and applied onto a flat background.
A sheet of coloured leather or a red cloth was often slid on the inside of this ornamentation in order to accentuate the carving. The main part was a clasp, which was fixed to the lid of the chest. When the lid of the chest was closed, this clasp would fall into place exactly on the face of the lock.
These locks, decorated with curious designs, rosettes, small columns, arches, niches, sheltering a crowd of tiny characters, were magnificent sculptures carved from the block, tailored with graver and chisel, and were as precious and valuable as the finest pieces of goldsmithing work.


Illustration : Iron key (12th century). The point disengages the lock mechanism.