It is logical to say that they were used to open and close the doors of the houses of our ancestors, but not only that, but there were also smaller key rings, these were used to open and close boxes or chests.
Undoubtedly a great invention and an easy and functional way of not losing the house keys, although comfortable to wear we do not know if it would be, but we must remember that the clothes they used at that time did not have pockets. It is likely that they could also wear it hanging from the ring itself.