Teuta, Queen of Illyria (today’s Balkan Peninsula) orders the execution of Roman ambassador Coruncanius. The queen’s flagrant violation of the law of nations incensed Rome, prompting the First Illyrian War (229–228 BCE). (Chronicle/Alamy Stock Photo)
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In international conflict, most belligerents have long recognized the tangible benefit that exists in mutually recognizing and adhering to the idea that certain persons should be immune from attack or molestation, even when those people are official representatives of the enemies. This is the concept embodied in the idea of diplomatic immunity, a modern phrase which has actually existed in different constructs for thousands of years.

The international law of diplomatic immunity in its current form was created in 1961 by the adoption of the Vienna Convention on Diplomatic Relations. The ideas formally codified at Vienna ensured the safe conduct of diplomats to facilitate communication between governments, “particularly during times of disagreement or armed conflict.”

That language would have been instantly recognizable to statesmen and jurists in both the ancient and medieval eras because their understanding of the concept was much the same, especially as it applied to three distinct categories of protected persons: heralds; envoys; and the embassies of official ambassadors.

This Is Sparta?

In the ancient world, prior to any formal codification of law pertaining to diplomatic immunity, religious practices provided the foundations of the protections afforded to designated people. Priests or other persons of religious affiliation often served as official envoys between states, and their status as clerics was the first basis of immunity. To attack or harm an emissary, even one from a hostile nation, was to risk offending the gods upon whose favor might turn the fortunes of war.

So, while the Spartans really did throw a Persian emissary into a well in 491 BCE after he demanded of them “earth and water” as tokens of their submission to the emperor Darius, they quickly repented of the act after deciding they had insulted the gods by doing it.

The Spartans sent their own emissaries to Darius with the offer that he could execute them to remit the offense, but the Persians were by then irrevocably committed to war. Athens had dealt with Persian envoys in nearly the same way, but the Athenians were apparently less troubled by the idea of divine retribution for the killing of official emissaries.

With the ascendance of the Roman Empire, the widely recognized tenets of guaranteeing the safety of diplomatic missions were increasingly codified into law. Drawing on the idea of ius gentium, or “the law of nations,” the Roman jurist Gaius wrote that “the law that natural reason establishes among all mankind is followed by all peoples alike, and is called the law of nations as being the law observed by all mankind.”

Immunity—At Least In Theory

It was an idea that should govern all human conduct, because all humanity recognized its importance, regardless of their societal or political differences. A later Roman jurist, Hermogenianus, developed this concept further by specifying that ius gentium applied in matters of “war, national interests, kingship and sovereignty,” as well as other areas that would today be classified as commercial law. A particularly important detail in the Roman view on the question, one which was to shape nearly every aspect of later medieval thought, was in the idea of the bellum iustum, or “just war.” Roman commentators went to extraordinary lengths to explain why their numerous wars, large and small, were all justified, and one of the essential elements of a just war was that it must be preceded by a formal declaration of war by duly appointed officials. Once those conventions were observed, a war was justified and could be prosecuted to the fullest, and most savage, extent necessary, but the persons who brought that declaration of hostility were to be immune from retaliation.

It was considered an egregious offense in both legal and religious terms to harm a diplomatic envoy, even after a state of war existed, but beyond the religious views that dictated proper treatment of envoys, another more pragmatic motivation was always in play—reciprocity. 

Even the most belligerent of ancient rulers seemed to hesitate to mistreat his enemy’s ambassadors for the simple reason that he wanted his own ambassadors to be able to carry out their diplomatic missions unmolested.

The familiar image of ancient despots ordering the execution of their messengers who were unlucky enough to bring bad tidings was actually more of a domestic issue when it occurred, rather than an international one.

Most rulers were careful to safeguard the immunity of foreign emissaries as a practical means of ensuring the safety of their own envoys who represented their interests in foreign courts.

The Need for Parlay

In the early medieval period, European jurists built upon the Roman concepts of ius gentium and further formalized it under canon law. As the early scholar Isidore of Seville wrote, ius gentium was understood to pertain to nearly all practices of war including occupying enemy territory, fortification of strongholds, the taking of captives in war, the negotiations of treaties, and, most important to this discussion, “the inviolability of ambassadors.” That this was an almost universal truth, he declared, was obvious “because nearly every nation uses it.”

This was not to say that all noncombatants enjoyed the same level of protections from harm. “The laws of war in the Age of Chivalry knew something about the immunity of noncombatants,” as one historian has observed, “though what they knew they usually ignored.” This was true of civilians and sometimes even clergymen who were unlucky enough to cross an invading army’s path, but it was not usually true of heralds, envoys, or ambassadors.

Even in this stage of diplomatic practice reciprocity continued to play its part, especially in the observance of formal truces between combatants. Since one party to a truce was considered released from restraint if the other party broke the agreement first, self-interest continued to be the best check on aggressive impulses. 

Roman concepts continued to exert strong influences over medieval European ideas of the proper ways to engage in warfare, and the notion of just war remained central to most of the formal wars that pitted one realm against another throughout the Middle Ages.

Carrying White Wands

A Christian king could not claim God’s blessing on his wars against his neighbors unless he first declared his belligerent intentions by means of a formal declaration of war, which in that era took the form of the diffidatio, or formal “defiance,” delivered in person by an officially designated and recognized representative. This was most often the function of the herald.

Heralds served several roles in the medieval world, both in times of war and peace, but they were frequently tasked with carrying messages of defiance between warring kings, or between kings who were about to go to war with each other. In an era when dress and insignia carried great significance and were increasingly regulated, heralds carried white wands or batons as a visible sign of the immunity inferred upon them by their positions and diplomatic missions. Henry V’s 1415 campaign into France, which famously culminated in the Battle of Agincourt, offers an excellent example of how scrupulously the protections of heraldic immunity were usually observed during medieval warfare.

After completing his siege of Harfleur, Henry marched his army through the French countryside enroute to his embarkation port at Calais in a symbolic declaration of his right to the territory he claimed. In response, the French sent three heralds to tell him that they would bring him to battle and destroy him before he reached safety. One of those heralds was a man named Jacques de Heilly, who had been captured by the English in an earlier battle (in which he was not serving as an officially appointed herald) and who had managed to escape and return to France.

Carrying the white wand and wearing a herald’s surcoat, de Heilly clearly did not have any hesitation about walking into the midst of the English army, even though he was recognized and under any other circumstances would have been subject to recapture. If he had broken his parole in order to affect his escape, he would even have faced the possibility of execution if he fell back into English hands. As an official herald, however, he could pass in and out of Henry’s forces without fear of molestation, and did so. 

De Heilly’s case provides another truth about how heraldic immunity functioned in practice. He was killed a few weeks later in the chaos of the fighting at Agincourt, even though he was then marked as a herald. Whether he was deliberately targeted or struck down by chance in the maelstrom of battle is uncertain. 

Just as they were essential to the formal declaration of war, heralds were also integral to the aftermath of battle, whether they were on the winning side or the losing side. After Henry V won the day at Agincourt, he summoned both English and French heralds to determine what the location of the battle was, to set the name by which it would be recorded in both his exchequer records and in the histories.

The French heralds declared that the battle was indeed an English victory, thereby formalizing the outcome. The heralds on that field were also responsible for making the tally of the fallen, taking a record of all men of chivalric rank killed in the fighting. The common rank-and-file soldiers of both armies were less important, other than to ensure that the paymasters could strike their names from the muster rolls.

Legalized Spies?

While heralds held the status of protected messengers, they were not diplomatic negotiators, and their role in that sphere was usually just to secure guarantees of safe conduct for the official embassies that might be sent after them.

“Heralds lacked the status and were not expected to have the expertise to qualify them to act as ambassadors,” as one scholar notes. To put it another way, heralds provoked the fight; ambassadors negotiated the peace treaties and armistices that followed the fight. For that critically important role, noblemen and senior clerics were called upon since they were far better versed in matters of law and statecraft, and their rank was a mark of the respect paid to the courts that received them.

In the rough and tumble world of medieval conflict, ambassadors from a hostile nation were often regarded as “legalized spies,” but their immunity was usually considered inviolable, even if grudgingly so. A full century before Agincourt, Honore de Bouvet, consellier to the French king Charles VI, wrote, “according to written law, ambassadors and legates pass in security through a country, and while they are going to the king outside the realm, no man may hinder, disturb, or injure them.”

Their protected status was considered unbreakable even in times of extreme provocation, such as when one party to a peace treaty violated its terms. The aggrieved party in such a betrayal “could offer no violence to the enemy’s envoys, they being protected by the Law of Nations and declared inviolable and sacred apart from any agreement or a truce and even in the heat of war,” the Spanish chronicler Ayala declared, and concluded, “it is immaterial that the enemy have already broken a truce and done violence to envoys sent from the other side to them.”

This understanding of diplomatic immunity continued into the Renaissance, as demonstrated by the fact that the Spanish ambassador to the court of Elizabeth I continued to have regular access to the English seat of government even though he represented England’s greatest and most dangerous enemy.

These millennia of thought and practice formed the basis for modern concepts of diplomatic immunity formalized in the 1961 Vienna Convention.