The air in the grand, stone-hewn halls of medieval Europe was thick with burning incense and silent conspiracies, but beneath the fragrant smoke lurked a deeply rooted paranoia—a suffocating fear that haunted the highest thrones and the lowest hovels alike. Today, the very word sends an instinctual shiver down the spine. For most of the modern world, incest is universally seen as a forbidden, deeply unnatural sexual intimacy between anyone who is intrinsically related by blood, such as a parent and a child, siblings, or cousins. In our current era, we could even reasonably extend this profound taboo to include anyone who holds a position of trust, authority, and responsibility within a family structure, such as stepparents, step-siblings, or aunts and uncles who have married into the fold. It is a boundary of nature, deeply ingrained in our collective conscience. Yet, travel back in time to the shadowy, turbulent epoch of the Middle Ages, and you will uncover a twisted reality where bloodlines tangled in the dark, and the Roman Catholic Church developed an absolute, consuming obsession with this very subject. This was not merely a matter of simple morality; it was a devastating weapon of political power. The theological fixation grew to such staggering, fever-pitch proportions that it ignited bitter, world-altering arguments, pitting almighty Kings against infallible Popes in a vicious, high-stakes struggle for control over the human soul and the royal bedchamber. Welcome to a dark and scandalous journey into Medieval Madness. Prepare to step into a world where the lines of love, lust, and divine law were blurred beyond recognition, where the marital bed was the ultimate battlefield, and where your own family tree could become a death sentence to your worldly ambitions.
Many forms of intimate sexual contact that we regard as completely normal and healthy today were strictly considered by the medievals as unnatural and deviant. The dogmatic, unyielding view of the era dictated that sexual contact was solely for the divine, utilitarian purpose of procreation. It needed to be strictly confined between a lawfully wedded husband and wife, and usually, it just involved the standard missionary position. Anything else that deviated from this rigid, joyless framework was starkly condemned as sodomy. As the centuries crept forward, the all-powerful Church became just as fiercely obsessed with the concept of incest as it was with the perceived sins of sodomy.
The first ominous whispers of this creeping obsession were officially documented when incest was first mentioned in the rigid Canons of the Council of Orléans in the year 511. The momentum of this moral crusade built rapidly, and just six years later, the strict Burgundian Council laid down the law with an iron fist. They vehemently forbade marriage to a staggering array of relations: a brother’s widow, a deceased wife’s sister, a mother-in-law, a cousin, the child of a cousin, an uncle’s widow, or a stepdaughter. The net of forbidden love was cast incredibly wide.
In the year 516, a dramatic scandal rocked the clergy when the Bishop of Grenoble was ruthlessly reported to his superior for the crime of marrying his dead wife’s sister many years previously. Unsurprisingly, after sharing his life with his wife for thirty long years, the Bishop outright refused to divorce her, standing defiant in the face of ecclesiastical wrath. Nevertheless, the cold eyes of the Church viewed the marriage as fundamentally incestuous, and decreed that it had to end. This tragic, highly publicized case was a possible trigger for the Church’s intense, unyielding interest in policing incest that relentlessly followed.
It was Augustine who arrived from Rome in 597, bearing the heavy burden of christianizing the fierce Anglo-Saxon pagans. The ancient custom of the Anglo-Saxons to freely marry their close relatives deeply bothered Augustine, threatening his rigid Roman sensibilities. In a state of moral panic, he wrote to Pope Gregory the Great, desperately asking for divine help with the problem. Augustine, who later ascended to become the very first Archbishop of Canterbury, urgently needed to know to what exact degree a Christian should be allowed to marry their kin.
Gregory pondered the fate of the English souls and ultimately decided that it was absolutely not permissible for any persons to marry who were related within the third or fourth generations. This was a monumental decision that he claimed to have made based on both:
“Experience and scripture.”
Although the Pope astutely recognized that the English had so many of these cross-family unions already established, he decided it was probably best just to sternly warn them not to do it in the future because it was a profound evil. However, in a rare show of political pragmatism, he chose not to brutally punish them for:
“Sins which they committed through ignorance before they had been converted to Christianity.”
The medieval Catholic Church was a hugely powerful, monolithic entity that dominated the whole of European society in the Middle Ages. Every aspect of daily life, from birth to the grave, was shrouded in its dogma. According to the teachings of St. Augustine, marriage was not merely a physical union but a deeply spiritual concept that actually altered a person fundamentally, making their two separate souls into one singular flesh. Therefore, religious zealotry was probably a major factor in what rapidly became a tyrannical obsession with incest.
However, one must look beneath the veneer of piety. Policing marriage was an incredibly effective way in which the Church could assert its absolute position of authority over the common people and nobility alike. Furthermore, it may also have been a highly calculated method of gaining significantly more wealth. After all, wealthy landowners and terrified nobles were far more likely to leave their vast money, lands, and earthly possessions to the ever-expanding Church if their marriages were annulled and they didn’t have any legitimate heirs who could legally inherit.
By the time the 9th century dawned, the Church in Europe had grown exponentially in both wealth and political influence, and it now heavily dictated the subject of marriage. The early Bishops of the Frankish churches fixated intensely on the complex subject of consanguinity—the state of having direct blood kinship with relatives. They became increasingly restrictive, ramping things up by implementing draconian incest laws across the breadth of Europe. This radical shift meant that the prohibited degrees of separation in relationships dramatically increased from four degrees to a staggering seven. That sweeping mandate meant absolutely no marriages between in-laws, members from a step-family, or even second cousins.
In the year 721, Pope Gregory II took the paranoia a step further, issuing a strict papal ban on marriage between those who were seen as having “spiritual kinships,” such as godparents. The web of forbidden connections grew ever tighter. Actually, it was only when the world finally reached the intellectual shifts of the 12th century that the Church finally managed to come up with a clear, codified view of what a marriage really, legally was. They meticulously defined what a couple precisely needed to say out loud to be considered married, and firmly debated whether the marriage physically should be consummated to make it a legally binding union in the eyes of God.
Perhaps it would make things a little easier to comprehend if we gave a quick, definitive rundown of the complex degrees of consanguinity and what they realistically meant for the terrified medievals trying to find a mate. It is, of course, the first degree of consanguinity that is the absolute closest, being the direct bond between a parent and a child. Second-degree kinships are the close bonds between siblings. Third-degree connections are those between an uncle and a niece, or an aunt and a nephew.
The web expands from there, with the fourth degree being first cousins. The fifth degree broadly includes great-grandnephews, nieces, aunts, and uncles. The sixth degree encompasses second cousins, and finally, the seventh degree stretches all the way out to second cousins once removed. Now that we’ve cleared that dizzying genealogical math up, you really have no excuse for choosing the wrong spouse!
These convoluted degrees of separation were meticulously calculated by counting back through the ancestral generations to find a single common ancestor. With marriage between anyone more closely related than a seventh cousin now strictly prohibited by law, it became a desperate, daily struggle for the nobility to find anyone of their own high status to marry. Participating in a sneaky, clandestine marriage behind the Church’s back was a massive risk; if discovered, it would result in the union being instantly nullified and the children branded as bastards.
Trying to find a potential, suitable spouse outside of the thousands of people that you inevitably shared at least a few stray genes with became harder and harder as the centuries dragged on. Over the years, a lucrative loophole emerged: many wealthy couples were given a handy, quiet dispensation from the Church—as long as the price of gold was right. With these bought-and-paid-for exemptions becoming more and more of a common occurrence, Pope Innocent III finally saw the logistical nightmare for what it was. He practically reduced the degrees of separation back down from seven to four again in the pivotal year of 1215. He recognized that finding more distant relatives to marry was often remarkably difficult and sometimes mathematically impossible for the insular noble classes. But even with that merciful reduction, it still meant being strictly banned from marrying anyone who had the exact same great-great-grandparent, which heavily covered more than just your standard first cousins.
There was a marked, aggressive increase in Church involvement in private marriage practices during the turbulent 11th century. Throughout the entirety of Christendom, people were strongly encouraged to build elaborate family trees that would supposedly prevent any accidental incestuous unions, a practice dating from as early as 948. But with the rare exception of the most elite aristocratic families who kept meticulous records, most ordinary medievals didn’t have a single clue who their distant blood relatives actually were. Consequently, many peasants and merchants who happily married were completely oblivious to the hidden fact that they were distantly related at some obscure point in their family’s unwritten history.
To combat this, in the 13th century, wedding banns began to be publicly and loudly announced in the town squares, declaring two persons’ clear intentions to marry. This public broadcast meant that others in the community would have a fair chance to speak up and object to the union if they truly believed that there was any hidden, familial impediment that should forcefully stop a marriage from going ahead. Parish priests were also actively encouraged to act as ecclesiastical detectives, ordered to carry out their own thorough investigations into any betrothed couple’s murky kinship.
The battlefield of marriage often pitted the papacy directly against the monarchy. In 990, Hugh Capet, the ambitious ruler of the Frankish throne, strategically arranged a political marriage between his young, 15-year-old son, Robert II of France, and Rozala Susanna, the noble daughter of King Berengar of Italy. But the manufactured union was a miserable failure, probably due to the glaring fact that Rozala was much older, being 38 at the time of the wedding. They bitterly separated after just a single year.
Then, in 996, Robert defied convention and married his own first cousin, Bertha, who was the grieving widow of Odo I of Blois and the daughter of the King of Burgundy. But Pope Gregory V was absolutely furious. He loudly declared the royal marriage to be entirely invalid and ruthlessly condemned it simply because she was Robert’s first cousin. Robert, who was internally a pretty God-fearing guy despite his royal rebellion, was deeply, spiritually troubled by this papal condemnation. Yielding to the pressure, he separated from his beloved Bertha. As punishment, the unforgiving Pope gave the King a grueling seven-year penance to suffer for his wicked sin.
In 1004, a weary Robert was married for a third time, this time to Constance of Arles. But his heart still tragically hankered after Bertha. Driven by lost love, he actively tried to annul this third, unhappy marriage and desperately attempted to have another valid marriage with Bertha again. By this time, the papal throne was occupied by Pope Sergius IV, and much like Gregory before him, he stubbornly refused to acknowledge the validity of the proposed nuptials, leaving Robert brokenhearted.
Marriage among the elite was always a convoluted family affair. The legendary Eleanor of Aquitaine was strategically married to Louis VII of France in 1137 at the tender age of 15. She possessed an incredibly vast domain, making her one of the most politically powerful and fabulously wealthy women in the entirety of Western Europe. But by the dramatic 1150s, the royal couple had become bitterly estranged. Coincidentally, Eleanor’s dangerously close relationship with her charismatic uncle, Raymond, the ruler of Antioch—a relationship which was whispered in the dark corners of the court to be one of “excessive affection”—certainly wasn’t helping the dire marital situation.
Louis and Eleanor’s highly publicized annulment by Pope Eugene III was ultimately granted on the convenient grounds of consanguinity. The Church lawyers proved that they were both directly descended from Richard II of Burgundy and his wife, Constance of Arles, technically making the King and Queen fourth cousins.
But the ink on the annulment was barely dry when, just eight short weeks later, the fiercely independent Eleanor shocked the continent. She married Henry Plantagenet, the fiery future King of England. The grand irony? He was also her fourth cousin. Henry was similarly descended from the bloodline of Richard II and Constance. Furthermore, looking deeper into the tangled ancestral web, Eleanor and Henry were also half-third cousins because of Ermengarde of Anjou, who was yet another shared common ancestor. So, in a spectacular twist of fate, Eleanor was actually even more closely related by blood to her second husband than she ever was to her first! Not to be outdone in the realm of marital hypocrisy, Eleanor’s first husband, King Louis VII, also rushed to marry someone whom he was even more intimately related to after their bitter divorce. Constance of Castile was his own second cousin, and they lavishly celebrated their royal wedding in 1154, with the Church turning a convenient blind eye.
When it came to navigating the terrifying laws of medieval incest, it really wasn’t about what you knew; it was entirely about who you knew and how much power you wielded. Even the historically monumental marriage of William the Conqueror to Matilda of Flanders was heavily tainted by the dark brush of incest. They were widely said to be related within the forbidden three degrees.
In 1051, at the time of their grand wedding, when William was still fiercely fighting as just the Duke of Normandy, Pope Leo IX decided he fiercely wanted to flex his supreme papal authority. He boldly prohibited the royal union. But the powerful Duke and his bride audaciously did it anyway. As a result, they were severely put under an ecclesiastical ban, isolated from the spiritual graces of the Church.
However, the political tides eventually turned. Later, a more pragmatic Pope Nicholas II gave the defiant couple a highly sought-after dispensation and officially legitimized their controversial marriage in 1059. The catch? The divine forgiveness came with a massive architectural price tag. They were pardoned only because they solemnly promised to build and fully fund massive new religious structures. Accordingly, a magnificent new monastery and a sprawling abbey and nunnery were swiftly built in Saint-Étienne and Sainte-Trinité. These grand testaments to bought forgiveness were beautifully consecrated in 1066, just moments before the ambitious William set off across the treacherous waters of the English Channel on his legendary, successful conquest for the English Throne.
Throughout the era, some cunning rulers deliberately brought up the technical impediment of incest as a brilliant, if underhanded, legal loophole to get rid of an unwanted spouse. Most famously, though slightly later in history, King Henry VIII of England notoriously tried to use the technical fact that he had married his dead brother’s widow as solid theological grounds for a desperate divorce from Catherine of Aragon. Incidentally, Henry was actually related by blood to every single one of his six ill-fated wives to some varying degree, but the dramatic Tudors are a little out of our current medieval timeline.
Much earlier, in the late 11th century, and after suffering through a strained 20-year marriage, King Philip I of France had aggressively tried the exact same cunning tack. He suddenly claimed that there was an unacceptable degree of incest between him and his long-suffering wife, Bertha of Holland. The truth was far less pious: Philip simply wanted to passionately marry the beautiful Countess Bertrade of Anjou instead.
But the papacy and the senior French clergy were not fools. They furiously charged Philip not only with blatant adultery—because Bertrade’s lawful husband, Count Fulk, was still very much alive and breathing—but also with the grave sin of incest. After all, the King was actually related by blood to the powerful Count. The arrogant King threatened to violently throw the protesting French clerics into dark, damp prisons. In utter defiance of God and man, Philip and Bertrade married anyway. In retaliation, a furious Pope Urban decisively excommunicated the stubborn King, condemning his soul to eternal damnation. After a grueling, 12-year political and spiritual fight, where the tumultuous couple separated and tearfully reconciled on several dramatic occasions, the exhausted French King finally gave in to the overwhelming pressure of the Church and formally agreed to forever end all intimate intercourse between them.
Other tragic, politically motivated instances of consanguinity which occurred during the dark span of the Middle Ages included the ill-fated tale of Alfonso IX of León. He proudly married Berengaria of Castile in the year 1197. However, the very following year, their joy turned to ashes as they were brutally excommunicated by the powerful Pope Innocent III. This happened even though their high-stakes marriage had been painstakingly arranged as a desperate, necessary way of finally securing a lasting peace between the warring factions of Alfonso and Berengaria’s father. The desperate couple spent years frantically trying to get a papal dispensation, offering wealth and loyalty, but the unyielding Pope flatly refused. Under the terrifying, constant threat of eternal excommunication, and despite the heartbreaking fact that they had already joyfully brought five children into the world together, the sacred union was officially voided and tragically ended in 1204, although they were miraculously able to somehow establish their innocent children’s legal legitimacy.
The tangled roots of royal family trees continued to strangle many lineages. Richard III of England married his own first cousin once removed, Anne Neville, as her great-aunt was actually Richard’s own mother. The world-famous, immensely powerful Isabella I of Castile and Ferdinand II of Aragon were themselves second cousins, as they were both directly descended from the bloodline of John I of Castile.
And finally, to truly witness the catastrophic endgame of these policies, one only has to look at just one of the many shocking intermarriages from the doomed Habsburg dynasty. This tragic saga involves Philip II of Spain in the turbulent 16th century. In his desperate quest for an heir, he had four different wives. His first bride, Maria Manuela, was unbelievably his double first cousin. His second wife, Mary I of England, was his double first cousin once removed. His third wife, Elisabeth of Valois, offered a brief genetic reprieve, as she was only distantly related. But his fourth and final wife, Anna of Austria, was an absolute genealogical nightmare: she was not only his direct first cousin but also, horrifyingly, his very own niece.
It was the mighty Habsburgs’ countless, unchecked years of extreme, incestuous interbreeding, driven by a paranoid desire to keep power entirely within the family, that ultimately caused devastating physical and mental deformities in their family members. This toxic concentration of bloodlines was the very poison that was probably responsible for their ultimate, tragic disappearance from the grand stage of history altogether.
