A unique intricate miniature box lock made of gold and iron from the Roman period has been discovered in Petershagen, North Rhine-Westphalia, Germany. Just 1.2 by 1.1 centimeters in dimension, smaller than a one euro coin or a U.S. quarter, the tiny lock dates to the 3rd or 4th century. It is the northernmost box lock ever found in Germany and the only miniature one ever found in Europe.

It was found in a field by licensed metal detectorist Constantin Fried in 2023. He reported the find to experts at the Westphalia-Lippe Regional Association (LWL) Archaeology for Westphalia who recognized it as identical to Roman locks used to secure boxes and caskets, but much smaller and gold instead of the usual iron or bronze.

The casing of the lock was made of two cylindrical metal sheets closed with caps at the top and bottom and riveted. The outermost sheet is decorated with two rows of perforations. The chain is missing, but the end link from a chain is visible inside the lock, as is a rusted iron core. Seeing that, LWL conservators decided to explore the innards of the micro lock to see if it was actually a functioning mechanism instead of a decorative miniature.

X-rays and CT scans could not penetrate the dense casing and only showed the rivets and chain end link, so the team deployed the more powerful 3D neutron computed tomography technology to see into the lock.

The image quality of the neutron CT provided the research team with the key to understanding the iron mechanism in the miniature lock: the cross-sections show a frame with a spring and presumed guide rail, a bolt, a base plate and a pin. “They also showed that the mechanism is largely complete but damaged, because someone had obviously poked around in the lock at the time, probably to break it open or to remove a blockage,” says finder Constantin Fried, who kept up to date with the ongoing investigations into his most significant find to date.

“Despite the damage, the function of the mechanism and the lost key could be easily reconstructed, because the shape and dimensions of the components allowed conclusions to be drawn. But comparative finds also helped here,” explained Rind. A restorer from the LWL Archaeology Department has made a fully functional replica of the lock, four times larger than the original. Rind: “With the chain end link still in place, it was also possible to reconstruct a link chain for the lock, which must have had at least six elements for the lock to work.”

“The extraordinary find from Petershagen shows the high level of craftsmanship of the provincial Roman blacksmith and metalworking trade,” says Rüschoff-Parzinger. At the same time, the find gives the LWL archaeologists new clues about the relationships between the local elites in Westphalia and the Roman Empire, as well as the possible local significance of its site.