How did Roman ring keys work?

Roman ring keys were a significant innovation in the history of security, representing the first instance of small, portable keys that could be worn on the fingers as rings.1

These keys functioned within the context of the warded lock, a Roman invention that utilized wards—internal projections around the keyhole. To operate the lock, the key's flat face, or bit, required specific slots cut into it. These slots allowed the key to bypass the internal projections so it could be rotated to engage the mechanism.1

While the Romans were highly ingenious in designing these complex ward patterns to ensure only the correct key could operate the lock, the security of these devices was limited. Because the mechanism relied solely on these projections, the locks were relatively easy to pick using instruments designed to clear the wards.1