I’ll admit it: this particular essay is kind of a grab bag of random techniques and technologies people have historically used to protect their belongings. But I think they merit discussion because our imagination in this regard often stops are locks and walls and guards, when the truth is that our ancestors were so much more creative than that.
Let’s start with puzzles. In a sense, that’s what a physical lock is; it requires the user to move pieces into the correct positions before the lock will open. But that kind of puzzle expects you to “solve” it by having something — the key; a code — that will make the entire thing easy to open. Something like a puzzle box, by contrast, has to be solved properly each time. Which means you can’t just steal the key; you have to know the right moves and execute them correctly to get the box open. The Romans sometimes combined this with locks in the form of puzzle rings; those require both the key (which might also be worn as a ring) and a secret move or two before they’ll open.
Closely related to puzzles are hidden compartments. They rarely work quite the way we see in movies (especially in the case of ancient temples whose wooden and rope components have mysteriously not rotted away), but they are real things; my husband’s paternal grandfather, who did carpentry for fun, included hidden compartments in almost every piece of furniture he made. On a smaller scale, so-called “poison rings” are often obvious (and not generally used for poison), but lockets of various kinds could be fairly subtle. On the larger scale, Catholics in England built priest holes to conceal the clergy of their faith; the Underground Railroad used similar devices, as did Europeans who hid Jews from the Nazis during World War II.
How secure are such things? In the case of hidden compartments, their best defense is having people not even know the compartments exist. Once a searcher’s suspicions are raised, though, it’s often easy to suss out where the compartment must be, just by looking at the geometry of the building or furniture and figuring out where it doesn’t line up. The more difficult part is figuring out how to get into the extra space, as the mechanisms for opening them can be quite ingenious.
But at that point compartments are vulnerable to the same kind of attack as puzzle boxes: you can simply destroy the container. Which brings us back around to the difference between deterrence, detection, and response. A puzzle ring locked around the neck of a sack doesn’t stop you from cutting through the sack, but it does make it obvious when someone has interfered with the contents, so nobody can steal a coin or two and hope it goes unnoticed. And in the case of things like smashing a puzzle box or cutting into a hidden compartment with an axe, you risk destroying whatever’s inside.
That notion of detecting interference also comes up in how we protect documents and mail. Cylinder seals are incredibly common finds in the archaeology of the Near East; they imprint an image onto soft clay, and were used as both a signature and a way of “locking” something so you could tell if it had been tampered with. Later in history we find different kinds of seals and sealing wax being used the same way, to the point where both signet rings and much larger official seals carried legal weight; for centuries England’s Great Officers of State have included the Lord Keeper of the Privy Seal (responsible for the sovereign’s personal seal) and the Lord Chancellor (responsible for the Great Seal of the Realm). (Though they’re stamps instead of seals for wax, Japanese inkan are used the way Westerners might use signatures, to verify legal documents.)
Again, these methods are aimed more at making intrusion detectable than preventing it entirely. As we all probably learned from books, though, a hot knife can potentially lift a wax seal without breaking it, allowing the intruder to read the contents of a letter and then return it to its original state. So they’re not very good security, right? . . . yeah, it turns out that our ancestors weren’t stupid. They knew wax seals weren’t very secure, and so they came up with better methods.
The simplest version involves folding your letter, punching a hole through the layers with an awl, and lacing thread through and around the letter before putting the wax seal on top of it. Now you have to cut the thread as well as lift the seal in order to read the letter — and since the thread is embedded in the wax, it’s much more difficult to replace it without the interference being obvious.
But they got even more ingenious than that. Based on the evidence of creases, cuts, and holes in old documents, some scholars have recently begun to study the practice of letterlocking: a marriage of wax, thread, and something akin to origami to keep letters safe. The dagger lock is especially diabolical, and I honestly don’t know how it could be defeated, short of forging the seal and the handwriting to make and close an entirely new letter to replace the one you trashed in the course of opening it. (But if you can think of a way, let me know!)
These kinds of things are neat. While it’s true that including a puzzle in a novel or short story might make it feel a bit like a video game, not everything has to involve making members of your adventuring party stand on specific platforms in order to open a door at the far end of the room. These devices can be smaller and subtler than that, especially with magic or futuristic technology to help. And it’s always fun to have a trick up your narrative sleeve, so your character can think they’re so clever prying into someone’s mail and then riiiiiiiiiiiiiip.