Sex, Spies and P.I.s: Which Profession Is Really the Oldest

When the phrase “the oldest profession” is uttered, most people instinctively think of prostitution. It’s a well-worn assumption, often repeated with a wink. But delve into the dusty archives of human history, and another contender quickly emerges—one that is just as enduring, perhaps even more influential: the profession of gathering information for others.

Whether under the banner of espionage or private investigation, people have long been paid to observe, eavesdrop, and uncover truths not meant for public ears. From ancient empires to modern democracies, the currency of knowledge has always held great value. In fact, the act of trading secrets may have been humanity's earliest form of organised power play.

German Spy Museum

Ancient Eyes and Ears

The role of the spy dates back thousands of years. In China, the military strategist Sun Tzu devoted a chapter of The Art of War to the use of spies, stating that good intelligence could determine the outcome of a war before a single arrow was loosed. Similarly, the Arthashastra, a foundational Indian treatise on statecraft from the 4th century BCE, outlined in detail how rulers should employ agents to infiltrate rivals and gather inside knowledge.

The concept was just as valued in ancient Egypt and biblical times. The tale of Rahab, who sheltered Israelite spies in Jericho, is but one early example of espionage operating at the intersection of faith, politics, and personal risk. From ancient Athens to the Roman Empire, intelligence gathering was not only common but often written into law and statecraft.

Private Investigation: A Parallel Legacy

Unlike espionage, which traditionally serves states and monarchs, private investigation has its roots in civilian concerns—property disputes, marital affairs, commercial fraud. Yet the two professions are close cousins.

The first modern private detective agency is credited to Eugène François Vidocq in 19th-century France, a colourful figure with a criminal past who went on to become a pioneer in investigative methods. Britain followed not long after, with Charles Frederick Field and Ignatius Pollaky offering investigative services to private clients, ushering in a more formal era of the profession.

As documented by Enigma Investigations, the private investigator has always evolved with the times—from the foggy alleyways of Victorian London to the digital age of cyber sleuthing. According to EJM Investigations, Queen Elizabeth I’s use of spies to protect her crown also marks one of the earliest recognisable examples of both state and “private” intelligence work blending.

A Tangled Web: When Professions Collide

Of course, not all spies operate in the shadows of state affairs, and not all private investigators remain behind the scenes. Sometimes, these roles overlap with other professions—most notably, the world’s alleged “oldest”: prostitution.

The Profumo Affair is a striking example of this crossover. In 1963, John Profumo, the then Secretary of State for War, became embroiled in a scandal after it was revealed he had been having an affair with Christine Keeler, a young model who was also involved with a Soviet naval attaché. The political and national security implications were profound. Sex, secrets, and state interests collided, creating one of Britain’s most explosive Cold War scandals.

In this instance, the intersections between intimate relationships and intelligence were stark. Keeler was not a trained agent, yet she found herself at the centre of a geopolitical storm. Her relationships had inadvertently created vulnerabilities within the British establishment—vulnerabilities that could be, and were, exploited.

The True Oldest Profession?

So, which profession can truly lay claim to being the first? The answer may never be clear-cut. What is clear, however, is that the pursuit and exchange of information is as old as civilisation itself. From the earliest tribal societies to the great empires of antiquity, those who could acquire and relay knowledge held a distinct advantage.

Sarah Saul, Managing Director of SIASS, puts it aptly:

“Whatever the 'oldest' profession may be, there is no doubt that throughout history humans have traded information. Knowledge certainly is power. Obtaining knowledge allows people to make informed decisions about courses of action open to them.”

This timeless truth underscores the enduring significance of both spies and private investigators. In every age, there have been those who wish to keep secrets—and those determined to uncover them.

Conclusion

While debates around the “oldest profession” are often played for humour or titillation, the serious history behind espionage and private investigation cannot be ignored. Both have shaped the course of nations, safeguarded interests, and exposed corruption. In their own way, they reflect something fundamental about human nature: our need to know, to understand, and to make decisions based on insight rather than ignorance.

Whether operating in the courts of ancient kings or the corridors of modern power, spies and investigators remain key players in the ongoing drama of human affairs. Perhaps, rather than trying to choose between them, we should recognise both as vital, historic—and enduring—professions.