Turn over the diplomacy rock, and you’ll find intelligence work underneath.
I’m using that phrase at the outset, rather than “spying” or “espionage,” because I want to be clear that intelligence work is far broader than what tends to appear in fiction. At its baseline, it’s simply the job of gathering intelligence — in the sense of information — to help guide your decision-making. We use it particularly in the context of such information gathered by covert means, but very little of that process looks like James Bond.
Modern intelligence services have a whole slew of abbreviations for the different avenues of collecting information: COMINT (communications intelligence, i.e. intercepting or eavesdropping on communication between people), IMINT (imagery intelligence, e.g. analyzing satellite photos), MASINT (measurement and signature intelligence, e.g. radar), and more. This kind of things appears a lot in TV and film because high-tech gadgets are appealing, these approaches often lend themselves to visual representation, and audiences are willing to skip over the time-consuming process of analysis to get to the conclusion. But even somewhat today, and especially in the pre-modern past, the dominant form was HUMINT, or human intelligence: information gained by talking to people.
Quite a lot of this doesn’t show up on the screen, or even on the page, because it boils down to passive observation and deductions based on what’s observed. An individual living in sixteenth-century Marseilles might report to his English masters that the number of Neapolitan ships in port is increasing — that might herald greater political closeness between France and Naples. He might pass along the news that the price of wool has risen sharply, because government agents have bought up large quantities of available stock — perhaps the French crown is preparing to outfit an army. He might even relay gossip that thus-and-such marquis has been rusticated to his country estate — and since said marquis led the pro-Spanish faction at court, this might signal growing disaffection on the king’s part for the prospect of Spanish alliance, or at the very least a gap through which a wedge of that sort might be driven.
Merchants are very good for this sort of thing, because their job requires them either to travel in person, or to deal with a lot of travelers. As such, they’re well-positioned to notice all sorts of details, and what patterns those details might form. This contributed to the negative image they had in many cultures; officials often assumed that all merchants were also spies on the side. Especially since it’s not necessary for someone to be formally on the payroll of another country — it’s enough for them to be willing to talk occasionally about what they’ve seen.
Technology has given us many more avenues for spying on other people’s communications, but that certainly existed in the past, too. After all, not every observer could report in person, and regularly traveling to and from a sensitive area was the kind of thing that attracted attention and questioning. I already covered codes, ciphers, and steganography in Year Three, so I won’t rehash that here, but the other side of that coin are the operations designed to intercept and decrypt letters between persons of interest. In the context of European history, these operations were often called Black Chambers, and they had to work fast: imposing too long a delay on the delivery of a letter might alert the recipient that someone had been meddling.
Not all intelligence work is purely about observation, though . . . and this is where we start wandering closer to James Bond territory.
Take those Black Chambers, for example. They didn’t merely read people’s mail; they might brazenly alter it so as to control the situation. The downfall of Mary, Queen of Scots in the Babington Plot was due in part to tactics a lawyer these days would decry as entrapment — including one of Walsingham’s agents rewriting one of Mary’s letters with additional material she had not penned (a request for the names of the conspirators involved). They considered this necessary to secure Elizabeth I’s hold on the throne of England, but their methods were profoundly sketchy.
Obtaining information not sent by post might require even more active effort. Here the methods are virtually indistinguishable from those of a thief, except that the spy often can’t afford to walk off with the documents; they need their target not to realize anything untoward has happened. In the absence of photography or some magical equivalent, they either need enough time to make copies — a slow and laborious process, when done by hand — or else a good enough memory to report on what they’ve read.
In many cases it may be safer and more effective to suborn someone with access, rather than breaking in yourself. Of course, dealing with traitors is dangerous in its own way: if they’ve sold out their current master to work for you, what’s to stop them from selling you out next? This is a perennially difficult question, then and now, with multiple possible answers. You can use money to sway someone to your side (but what if someone else offers more?), or ideology (but what if they lose faith or their nerve?), or blackmail (but now you have an asset who is merely frightened, not friendly) . . . none of the answers are a sure bet. The same can even go for your own people working undercover. In that case you at least start from a basis of more or less trusting them, but who’s to say how their loyalties may shift over time? Meanwhile, that agent runs a terrible risk, often facing death if they’re caught out.
I used to think that this field of activity was something every country engaged in as a matter of course. Then I read Rose Mary Sheldon’s Intelligence Activities in Ancient Rome, and discovered just how shockingly non-existent Roman intelligence work was, for how shockingly long. Even military intelligence, where you would justifiably expect them to excel! Well into the Republic, their method for receiving warning of an invading army consisted of “wait for a farmer in an outlying area to come running up with news.” It was entirely possible for their enemies to build up forces in secret, and the first Rome would know if it was when some town got sacked. They eventually improved — structures like Hadrian’s Wall are, among other things, surveillance posts for the surrounding countryside — but it seems even the Empire made surprisingly little organized, top-down effort to keep an eye on political affairs in neighboring lands.
Mind you, that’s history, which isn’t required to be as plausible as fiction. On the page, your readers may check out in disbelieving irritation when a general loses three legions to an ambush by his Germanic allies because he dismissed the single warning he received as nothing more than the product of a familial spat. (Sheldon’s book treats the Varian disaster as a massive failure of military intelligence.) But the upside to readers expecting more intelligent espionage is, that makes more opportunity for plot!