Governments have always valued information, but not all information counts as intelligence. In the middle ages, kings depended on travellers, such as merchants, pilgrims and heralds, to bring them political news of a kind that a later age would find on the front page of a newspaper. The use of scouts by field commanders is as old as warfare itself. They reconnoitred the terrain ahead or assessed the strength of enemy armies and reported on their movements. The people routinely referred to in countless administrative documents as ‘exploratores’ were generally scouts rather than spies. So, in spite of her use of the word, were the ‘espies subtyll’ which Christine de Pizan discussed in her Book of Fayttes of Armes and of Chyvalrye (ca. 1409); they were men whom every field commander should send out ‘for to enquire and understand the purpose of his enemies’.

True espionage, however, is more than mere reconnaissance. It is the art of discovering the enemy’s secrets. The systematic collection of secret intelligence began late in Europe. It was not until the 16th century that it became an ordinary tool of diplomacy and war. Before that, its collection was opportunistic and unsystematic. The challenges of intelligence-gathering were common to wars everywhere. But the long series of wars between England and France that took place from the 13th to the 15th centuries perfectly illustrate the techniques employed by the last generations before the creation of Europe’s first professional intelligence services.

The commonest method of obtaining secret information was also the crudest. It involved sending spies to listen out for gossip. Medieval courts were notoriously insecure. Crowds of courtiers, petitioners and mere gapers gathered in the open halls of royal palaces. There was very little control over entry or exit. Consultation was an essential part of the exercise of government, and many people were involved in decision-making process. Military encampments were no more secure: tent cities inhabited by thousands of soldiers, tradesmen, victualers and prostitutes, which were easily penetrated by strangers.

The main difficulty about this particular method of intelligence-gathering was language. Spies have to be able to fit in. Language, accent and dialect betrayed inquisitive outsiders even in a relatively homogeneous country such as Italy. The English were usually able to overcome this difficulty, for they had no shortage of French-speakers to call on. There were almost always Flemings, Hainaulters and French-speaking Gascons or French political exiles at their court. When Edward III was based with his army in the Low Countries between 1338 and 1340, members of the household of his French-speaking queen were regularly sent to listen out for indiscretions in Paris. Froissart tells us that the English planted agents fluent in English, French and German in the ranks of the French army.

As time went on, these operations became more sophisticated. In March 1386, when a huge invasion fleet was being prepared by the French in the ports of Flanders, the English sent a soldier of fortune from Hainault called Hennequin du Bos into France. He seems to have infiltrated the households of the Count of Saint-Pol and Jean de Sempy, the French governor of western Flanders, both of whom were involved in the logistical preparations for the invasion. His mission did not last long. He was caught snooping round Montreuil and eventually executed in Paris. The confessions extracted from him in the dungeons of the Châtelet prison were a mine of information about other English spies. At the height of their activity, in 1386 and 1387, they were operating across much of northern and western France. They picked up information by taking menial jobs in the households of prominent French noblemen. They wandered about the main recruiting and mustering areas disguised as horse-dealers, tinkers, cloth merchants, monks or soldiers of fortune. Their reports were passed by word of mouth to the English captain of Calais, who sifted the information and passed it on to the English ministers at Westminster. For more than 200 years Calais was a garrisoned English fortress on the coast of France, and an open window on events in France. The English administration there was probably the nearest thing to a professional intelligence service to be found anywhere in Europe at the time.

It was more difficult for the kings of France to recruit English-speaking spies. In the 14th century there was no anglophone community in France from which to recruit. English was hardly spoken outside Britain, even as a second language. In 1359 the Dauphin Charles, regent during the captivity of John II in England, succeeded in recruiting two Englishmen naturalised in France who secretly entered England, but they were soon identified as spies and orders given for their arrest. This was a rare case.

The English government believed that any French spies in England were more likely to be Frenchmen with some suitable cover story to explain their presence. They were travelling as merchants or couriers or belonged to one of the foreign mercantile communities in London. Monks belonging to the various French monastic communities scattered across England were another class of resident alien, perennially under suspicion. Occasional incidents seemed to justify their fears. In 1369 Jean Bocquet, the French prior of the Benedictine priory on Hayling Island was removed to an inland house after being caught with incriminating correspondence in his possession. This notorious case was cited in Parliament as a reason for closing down all foreign priories in England. The English authorities responded to the threat from enemy aliens by imposing tight control over ports of entry and lodging houses. They searched the baggage of foreign travellers. They closed the ports to civilian traffic in the build-up to major continental expeditions. There were periodic attempts to intern or deport aliens. In 1345 and again in 1380, Newgate prison in London was reported to be stuffed with suspected French spies. Most of this was paranoia. People arrested as spies were commonly sent for questioning by royal officials, but incriminating matter was hardly ever found. In 1380 no evidence could be found against any of the prisoners in Newgate, with just eight exceptions, all of whom were subsequently acquitted at their trial.

This kind of espionage was inherently unreliable. Spies tended to repeat gossip learned at many hands removed. They were keen to earn their pay by exaggerating their findings. Between 1384 and 1394 the Duke of Burgundy employed an elaborate network of spies run from the Flemish town of Mechelen by a person who is known only by his code name (‘the beardless man’). At least one of his agents was said to have been based in England, but the information he obtained was worthless. Most of it seems to have been derived from tavern drinkers in Calais, Flemish merchants in London or the talkative English community in the Dutch port of Middelburg. Likewise, the ‘special friends’ who reported from Flanders to the English royal council in 1435 on the Duke of Burgundy’s plans to attack Calais caused panic at Westminster, but their reports were a mixture of public knowledge and fantasies of their own invention.

The most reliable intelligence came from high-ranking traitors who were privy to the decisions of the kings and their captains. They had a variety of reasons for turning against their own governments. Crude bribery seems to have been rare. But a common factor was the remission of ransoms which perhaps came to the same thing. The ransoms exacted from rich prisoners of war could ruin them. There was always a strong temptation to turn spy in exchange for liberty. One of the earliest and most notorious cases was that of Sir Thomas Turberville, who was taken prisoner by the French in 1295 during the wars in Gascony. He was released by his captors in return for agreeing to spy for them. Once back in England, he wrote reports for the Provost of Paris on Edward I’s military, on the state of England’s coastal defences and on much sensitive political intelligence. Turberville was hanged after being betrayed by the messenger who he employed to carry his reports to France.

Grudges were another motive. Sir John Minsterworth entered French service after falling out with his commander during the disastrous English campaign in France of 1370, and then with the commission of inquiry appointed to consider the cause of the debacle. He was hanged, drawn and quartered. But even the horrifying penalties for treason were never enough to stop Englishmen from volunteering to spy for the French. In spite of the travel embargo and the mass arrests, Edward’s invasion plans of 1359 were leaked to the French king by someone in England who is described in French records as ‘exceptionally reliable and well-placed to know’. In 1372, when Edward III was planning what turned out to be his last military campaign, the French king was receiving detailed and accurate reports of his decisions. Their source was described by Charles V as ‘notable persons well-disposed to us in whom we have every confidence’. They were probably former prisoners of war or bribed officials.

The French administration was more easily penetrated than the English one, because for much of this period France was divided by civil wars in which the English sided first with one side and then with the other. There was therefore no shortage of disaffected people willing to work for an English victory. In 1336, as England and France were drifting into war, Philip VI secretly met two Scottish agents at Lyon and agreed to send an army to Scotland to join forces with a Scottish army and invade England across the River Tweed. Within weeks, an account of the meeting at Lyon was in the hands of Edward III’s councillors, together with a remarkably detailed account of the naval and military forces that the French planned to send across the North Sea. This information must have been obtained from some well-placed individual in the French king’s service. Two years later, a French traitor, or possibly an Italian in French service, was hanged for betraying plans to send a ship laden with weaponry and cash to support a Scottish attack on England. This information enabled the English to intercept the cargo at sea. ‘Can I not speak quietly in my private chamber without the King of England listening in?’, Philip VI once complained; ‘must he always be sitting there at my side?’ Philip’s successors had reason to echo his despair. The English ambassadors once told their French interlocutors in the closing moments of a diplomatic conference that everything that happened in the French royal council was at once reported to them.

Philip VI’s complaint was no doubt a figure of speech, but spies sent to mingle with the enemy did sometimes listen in to French planning sessions. In 1364 the Count of Foix repeated to Charles the Bad, King of Navarre, some information that he had learned from Charles V’s private secretary about the king’s plans to make war on England. They took the precaution of speaking out of doors in an enclosed garden, away from inquisitive secretaries and servants. But they were overheard from behind a wall by a French spy in English pay, who sent a detailed report to England. When the Duke of Orléans invaded the English duchy of Aquitaine in 1406, the English king’s seneschal and the city of Bordeaux organised an impressive intelligence network, which supplied frequent and generally accurate information about French plans. At least part of this information was obtained by a Gascon spy who was able to eavesdrop on the French commanders from outside their tents. Something rather similar must have happened in 1424, when the French king, Charles VII, was planning a major offensive in Normandy. His captains made their plans at their headquarters in Bourges and changed them several times. An anonymous spy in Bourges, presumably French, supplied the English regent, John, Duke of Bedford, with information that enabled the English to concentrate their forces in the right place at the right time. This was a significant factor in the disastrous defeat of the French army at Verneuil a few weeks later.

Intercepted correspondence was perhaps the most reliable source of information, for in it the enemy spoke in its own voice. Documentary security in the late middle ages was lax. Messages had to be written out and carried by runners or horsemen. Codes and ciphers were rarely used before the 16th century, and, when they were, they were generally extremely crude. The coded messages of England’s ally Charles the Bad, King of Navarre in the 1360s simply disguised proper names with pseudonyms, most of which could easily be guessed. In 1372 the French discovered the secret treaty between Edward III and the Duke of Brittany by intercepting the duke’s English wife on the road and rifling through her baggage. The capture of the English traitor Sir John Minsterworth by the English authorities in Gascony in 1377 yielded a rich haul of documents about the planned French invasion of Wales. In 1412, during the bitter civil war between the Armagnac and the Burgundian princes, the Armagnacs’ plans to ally with the English were exposed when their representatives were caught as they made their way to the coast to take ship for England. They escaped, but had to abandon their baggage, which was retrieved and found to contain their detailed instructions and a sheaf of blank charters.

Successful intelligence work calls for the experienced analysis of information from multiple independent sources. The accidental character of so much medieval intelligence made multiple sources hard to find, but without them there was no way of verifying the reports of inherently erratic agents or distinguishing between the authentic and the exaggerated or bogus. It also required a good understanding of the political and administrative context in which information was generated by an enemy, something which few states possessed before the age of resident ambassadors. English and French governments of the late middle ages were often astonishingly ignorant of basic facts about the politics of their enemies. This often made it hard to know what to make of those secrets they were able to discover. These were the principal defects of medieval intelligence-gathering. Sooner or later the problems would be identified and overcome, but it would take the great international wars of the 16th century and the dramatic increase in the financial and bureaucratic resources of the state.