The family of Habsburg between consanguineous marriages, legal restrictions, and biological consequences.

Bella gerant alii, tu felix Austria nube/ Nam quae Mars aliis, dat tibi Venus. …"Let others wage war, but you, fortunate Austria, marry/ Because what Mars (provides for the) others, divine Venus gives to you”.

This medieval latin couplet explains the rise of the Habsburg family – from minor Swiss counts to one of the leading royal houses of Europe ­– by the success of their dynastic marriage policy. Indeed, after establishing their power base in Austria during the course of the 13th and 14th centuries and being regularly elected Holy Roman Emperors from 1440 until 1806,  a series of dynastic marriages of young archdukes and archduchesses to members of other dynasties enabled the house of Habsburg to vastly expand its domains.

Among the first of these marriages was that of Maximilian, son of Emperor Frederick III., to Europe’s richest heiress, Mary of Burgundy, in 1477. After Mary’s death five years later, the Habsburgs received part of Mary’s rich inheritance.

In 1496 there was a double wedding between Spain and the house of Habsburg: the children of Ferdinand and Isabella, Joanna of Castile and Aragon, and her brother Don John, Prince of Asturias, were married to Maximilian’s children Philip and Margaret of Austria. The marriages were thus not part of some cleverly conceived Habsburg strategy for acquiring the Spanish throne, but rather a means of strengthening an alliance.

However, the double wedding was followed by a sequence of events that favoured the Habsburg cause: not only did Margaret’s new husband Don John die, but so did all the other Spanish royal heirs, putting Joanna and her husband Philip first in line for the throne. In 1500, they consolidated their claim to the succession by producing a son, the future Emperor Charles V, so that when Philip became king of Castile in 1504, Spain and all its possessions fell into Habsburg hands.

As if Burgundy and Spain were not enough, Maximilian I also wanted to expand his domains in the East. He arranged another double wedding between his grandchildren Ferdinand and Mary, respectively Anna and Louis from the house of Jagiellon, rulers of Bohemia and Hungary in 1515. Eleven years later, in 1526, after the death of King Louis (of Bohemia and Hungary) following the Battle of Mohács, both lands fell to the Habsburgs – but initially only in theory, because for one and a half centuries Hungary was split into three parts. Dynastic marriages were only one part of the medal: they gave claims to power, which mostly had to be confirmed on the battlefield. At the end of the 17th century, after almost two hundred years of war against the Turks, the Habsburgs did actually bring the whole of Hungary under their control.

As a result of this expansion, in 1521/22,“the Empire on which the sun never sets" was divided: the Austrian line of the Habsburgs held the title of Holy Roman Emperor and controlled the Habsburg hereditary lands in Austria and the kingdoms of Bohemia and Hungary, while the Spanish line ruled over the Spanish kingdoms including the Spanish colonies of the Americas, the Netherlands, the Habsburg possessions in Italy, and, for about 100 years, Portugal.

Numerousmarriages between these two family lines conserved the clannishness of the Habsburgs. Three of the five Habsburg kings of Spain ­married women from the Austrian family line, while three Habsburg emperors married Spanish Habsburg infantas. The purpose of these Habsburgintermarriages, was, of course, to ensure that the great double realm would remain within the family. If one side did not have enough heirs, it could  revert to the other. Furthermore, another more spiritual explanation has to be noticed : the mystical belief in the divine power of royal blood. For generations the Habsburg family held on very deeply to this archaic assurance. It meant that intermarriage among them only intensified the potency of that precious liquid.

This Habsburg marriage policy had some bizarre consequences. In the year 1570 King Philip II of Spain married his niece Anna of Austria, daughter of his sister Mary and his cousin Emperor Maximilian II. By doing this, Philip’s sister became his own mother-in-law, while Philip himself became his own children’s great-uncle. But the inbreeding had begun long before. Anna’s grandfather, Emperor Charles V, had already married his first cousin, and Anna’s father also had married his first cousin.

But beside these aspects, another primary goal of these marriages was to create legal heirs and to secure the succession. In the case of the Habsburg family, only one authority could raise an objection against this partly incestous dynastic policy: the Roman Catholic church. The Habsburg family and Catholicism were and still are closely linked today.  A missing papal approval for marriage could have had severe political consequences for both the couple and their supposed heirs.  But the canon law of the Catholic church sets definite rules for a valid marriage, which should have been unfavorable for dynastic interests in general.

Since the Fourth Lateran Council of 1215, canon law had forbidden marriages within four degrees, computed by counting generations back to the common ancestor:

        x
        __|__
       |     |
       x     4
     __|__   |
    |     |  |
    x     3  4
  __|__   |  |
 |     |  |  |
 x     2  3  4
 |__   |  |  |
 |  |  |  |  |
ego 1  2  3  4

In cases, where two individuals descended in an unequal number of generations from a common ancestor, the more distant descent governed the degree of consanguinity:

        x
        __|__
       |     |
       x     4
     __|__   |
    |     |  |
    x     3  4
  __|__   |  |
 |     |  |  |
 x     2  3  4
 |__   |  |  |
 |  |  |  |  |
ego 1  2  3  4
 |  |  |  |  |
 |  |  |  |  |
 1  2  3  4  5
 |  |  |  |  |
 |  |  |  |  |
 2  3  4  5  6

[etc.]

Subsequently, this very strict canon marriage law proved advantageous as a flexible instrument to support the political goals of the Roman Catholic church. The range of papal activity went  from prohibition or annulmentof marriages up to connivance, permission and secret or public promotion of certain marital unions.

Despite all legal interdictions, pope Pius V rapidly gave his permission to king Philip’s intra familial marriage with Anna of Austria. The appropriate papal document, today preserved in the Austrian State Archive, adjudges this matrimony a dispensation from all restrictions of canon marriage law, because the pope expected this liaison “to confirm and strenghten the real [Catholic] church and the expected indivisable alliance of Christian kings and rulers“. Therefore, Pius V connected his approval with two political claims: Philip’s dedication to  the Catholic Counter-Reformation and  the Holy league, an alliance of almost all the major Catholic maritime states in the Mediterranean, arranged by the pope in 1571 against the expansion of the Ottoman empire. Indeed, shortly after his marriage King Philip joined the League which set up a victorious fleet commanded by John of Austria, the illegitimate son of Emperor Charles V and half brother of King Philip II of Spain.

After the marriage of Philip II and Anna, the consanguineous Habsburg dynastic policy was continued. The son of this marriage was also named Philip, the third on the throne of Spain. He married Margaret of Austria, grandchild of Emperor Ferdinand I, who became both grandfather of the bride and great-grandfather of the bridegroom. In total, from the beginning of the 16th century until the year 1700 the Spanish Habsburgs arranged two uncle-niece marriages, one double first cousin marriage, three first cousin marriages, one second cousin marriage and two third cousin marriages. In total, 9 of 11 marriages were consanguineous unions in a degree of third cousins or closer.

Probably as a result of the long series of intra familial marriages, the male line of the Spanish Habsburgs became extinct in the year 1700, followed by the male line of the Austrian Habsburgs 40 years later. The last Habsburg on the throne of Spain, Charles II, was physically disabled, mentally retarded and disfigured. He also proved impotent since no children were born from his two marriages.

A group of Spanish geneticists analyzed the family tree of the Habsburg line from an extended pedigree up to 16 generations in depth and involving more than 3,000 individuals. Not only the Austrian and the Spanish line of the Habsburgs were analysed, but also the French Bourbons and the Portuguese house of Aviz. The scientists computed an inbreeding coefficient for every individual – a measure of the proportion of inbred genes inherited from the parents. The founder of the Spanish dynasty, Philip I, is calculated to have an inbreeding coefficient of 0.025, which meant that just 2.5 per cent of his genes were likely to be identical by common descent. But 200 years later, the coefficient had leapt ten-fold to 0.254 in the genome of Charles II, meaning up to one in four of his genes might have been identical.

As a result, the Spanish Habsburgs suffered a far higher percentage of child mortality than the general population, even though the family was immensely wealthy and did not experience the poverty related health problems faced by many people at the time. They also suffered a higher incidence of physical deformities, which are best exemplified by the famous "Habsburg jaw", a potentially disfiguring, genetic disorder, where the lower jaw outgrows the upper, caused by an inherited medical condition called mandibular prognathism.

Charles II additionally suffered from two genetic disorders, which caused sporadic hematuria and intestinal problems. He looked like an old person at the young age of 30, suffering from edemas on his feet, legs, abdomen and face. During the last years of his life he barely could stand up and suffered from hallucinations and convulsive episodes. His health got worse until his premature death when he was 39 after an episode of fever, abdominal pain, hard breathing, and coma.

After Charles’ II death, the kingdom of Spain fell to the crown of France – in spite of all longlasting familial connections and claims to inheritance by the Austrian Habsburgs. As usual in premodern Europe, decisions of this range of influence were not made in law courts, but on the battlefield.