In her recent book, The Astronomer and the Witch, Ulinka Rublack reveals how Kepler saved his mother from being burned as a witch. Using the original trial documents, Rublack brings to life the story of a small Lutheran community in the centre of Europe at a time of deep religious and political turmoil – a century after the Reformation, and on the threshold of the Thirty Years' War.


Here, writing for History Extra, Rublack explores Kepler’s long struggle to protect his mother from execution...

Some 73,000 people were tried for witchcraft and 40–50,000 executed in Europe between 1500 and 1700. More than half of all victims, around 22,000, were executed in the German lands from 1560 and three of every four witches executed during the height of European persecutions spoke some dialect of German. More than 75 per cent of those accused were women.

These are remarkable figures. To compare, the Spanish, Portuguese and Roman Inquisitions, with their highly centralised bureaucracies, are estimated to have carried out 300,000 trials against all kinds of heresy during the entire period of their activity, and to have executed around 13,860 victims. This means that far more people were killed in Germany as witches than lost their lives at the hands of these Inquisitions.

One of these women was Katharina Kepler, the 68-year-old illiterate mother of the famous astronomer Johannes Kepler, who was accused in the south-west German town of Leonberg in 1615. She vehemently denied the charge, and her family were equally outraged. Yet it took six years for the elderly woman to be acquitted, by which time she was so frail that she died within months.

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I came across this trial in the Württemberg state archives many years ago. Unusually so, the whole file seemed complete – archivists had even preserved Johannes’s letter protesting against payments for his mother's imprisonment. Reading the records gave me a sense of the vulnerability of an elderly women at this point in time and what was required to save her. The Keplers suddenly found themselves fighting to save their mother from a trial, torture, and the likelihood of being burnt to death. I encountered a family under intense emotional strain.

Johannes was at the height of his career during these years. He lived in the Austrian town of Linz and was filled with extraordinary confidence in his unique ability to understand God’s universe. He believed he had the insight to understand God’s building plans, his playfulness and jokes that manifested in nature. Creation to Kepler was about more than the laws of planetary motion he famously defined.

The trial of Kepler’s mother’s nonetheless threatened his ambitions. From the very beginning his tone was highly emotive as he set out to defend his own reputation at all costs. This was in part because the accusation implicitly raised the question of whether Johannes had been brought up to worship God or the Devil. His mother was not as remote from his world as we might now imagine. As he recalled, Katharina had once taken the six-year-old Johannes up a slope to watch a spectacular comet in the sky – clearly showing interest in cosmic change.

Furthermore, one of the charges raised against Katharina during the trial was that she had asked the local gravedigger to dig out her father’s skull, to emboss it in silver and send it to Prague, the city where Johannes served Rudolf II as imperial mathematician.


An execution of four witches in the 17th century. (Photo by Time Life Pictures/Mansell/The LIFE Picture Collection/Getty Images)

At the heart of the trial for Johannes Kepler thus lay an uncomfortable question he addressed in his most important book, The Harmony of the World (1619): To what extent was he like his mother?

In Book Four, chapter seven, Kepler set out how different they were, despite the fact that they had been born under an almost identical astrological constellation and shared the same physical constitution. Kepler explained that Katharina had not had the opportunity to receive any formal education. While pregnant, he alleged, his mother had begun to admire her mother-in-law and this woman’s father, both of whom had been popular healers.

Katharina’s behaviour thus needed to be explained through her female nature – through circumstance, but also through her particular temperament, which Johannes judged “certainly very restless”. He summarised: she “disturbs the whole of her town, and is the author of her on lamentable misfortune”. Kepler clearly felt resentful of his mother. Yet he did his utmost to defend her and it is unlikely that she would have survived had it not been for him.

On 9 November 1619 at 8am, witnesses assembled in Leonberg’s town hall. A schoolmaster reported that Katharina had been constantly pestering him to read out letters from or send greetings to Johannes. He claimed that one day she had by magic entered his house through locked doors as he and his wife were having dinner and had demanded that, there and then, that he should write a letter to be sent off to Linz, though he no longer remembered its contents.

Similarly, 10 years earlier, Katharina had asked the schoolmaster to come to her house and read several letters out to her. It was a Sunday, and he had wanted to go to church. Yet Katharina had detained him, pressing him to drink some of the good wine she had in her cellar to thank him. As he was not thirsty he had only sipped from the pewter mug, but Katharina kept prevailing upon him to drink more. Another woman joined them, swallowed most of her wine and had become so ill that she later died. The schoolmaster began to feel pain in his thighs the following day; next, he could only walk holding on to sticks. Now he was almost lame.

A woman named Dorothea Klebl also appeared a perfectly trustworthy witness. Born and raised in Leonberg, she was married to the local marksman. She knew that her age was roughly 33 (people at this time often did not know their exact age) and carefully replied to questions. Her answers revealed surprising as well as legally damning information. Five years ago, she said, she had employed a young local seamstress to carry out some needlework. Just before this time, this girl had worked for Katharina, who had once urged her to stay overnight. Deeply disturbed by the events that had followed, the girl confided in her new employer.

“Close to midnight”, the girl said, Katharina had risen from her bed to “roam about” in the main room of her house. As the seamstress woke up, she asked Katharina: “Why do you roam about in the chamber instead of lying in bed?”. Katharina replied: “Would it not please you to become a witch?”, promising the young girl “joy and debauchery beyond measure”. On earth, Katharina had allegedly declaimed, there was “neither joy nor spiritedness”.

On 7 August 1620, Katharina was first imprisoned in Stuttgart and then led to Leonberg for the beginning of a formal criminal trial. All the family’s pleading had been in vain. Her youngest son, Christoph, a local pewterer, was horrified. He could imagine only too easily the civic guard fetching his 73-year-old, now nearly toothless, small, white-haired mother from one of Leonberg’s prison towers, to take her on a chain or rope to the town hall, right in front of his house on the market square.

Every German execution was staged by local governments as a communal event, to admonish the people and make them pray for a poor sinner’s soul in eternity. Christoph wrote to Duke John Frederick of Württemberg at once, proudly relating that he had honourably learned his trade and even practised it with “particular fame”. The past five years of investigations against his mother had already been “extremely painful” to live through, he said. Now he feared “people’s open contempt”. Christoph Kepler demanded, therefore, that Katharina’s trial should be conducted elsewhere. The ducal chancellery decided to transfer Katharina to a small town called Güglingen, a town in Württemberg, about 60km south of Leonberg, a place she had never been before.

Christoph’s brother Johannes now moved to Württemberg as quickly as he could. He put his entire life on hold and packed up his household, his books and scientific instruments in Linz. He took his family with him to a halfway point by boat, where they stayed in Regensburg on the Danube. Kepler then rented a horse to ride alone on to Ulm and travelled up north to Stuttgart. From there he had to find his way up still further north and off the large trade-routes, asking for directions to Güglingen, where he knew nobody and few knew of him.


c1597, a diagram of a model by Johannes Kepler to explain the six planets in the solar system and their inter-relationship. Johannes put his life and work on hold to defend his mother. (Photo by Hulton Archive/Getty Images)

He arrived by the end of September. The famous mathematician was led to his old mother in the Güglingen tower. After three weeks imprisonment, she complained “bitterly” that she was cold, sad and lonely, and bereft of comfort. Johannes knew that he was now the only one of Katharina’s children who could help her. Following detailed conversations with his imprisoned mother, Johannes swiftly prepared a powerful, concise and clearly structured legal document in Katharina’s defence.

On 11 December, before the seasonal holidays, Johannes accompanied his mother to the Güglingen courtroom in the town hall. Governor Aulber read out the charges and confirmed his intention to conduct the trial quickly. The Keplers repeated their arguments questioning the legitimacy of a criminal trial. Then, Katharina was led back to her room and chained to the floor. This was how she would spend Christmas – imprisoned in a strange town.

Kepler’s lengthy legal defence first attacked the ability of many of the witnesses who had been interrogated in January to testify reliably; they were simply too young to rely on anything other than hearsay about his mother’s reputation. There was a strong legal requirement that a bad reputation needed to be well established before an accusation could be made. To establish factual evidence for his defence from superior male witnesses [males were more highly trusted], Kepler had read the depositions closely and now referred to testimony from old Hans Beitelsbacher and the saddler Michael Stahl, both of whom had been reputable members of the court and old enough to have known Katharina for most of her life. They had never thought of her as a bad woman.

Further, Kepler argued, it was one thing to enter people’s houses [as in the case of the German schoolmaster] and quite another to be a witch. Any association between these two would make any old, garrulous and frequently disliked woman vulnerable to this far-fetched accusation. Indeed, women considered to be behaving strangely should not automatically be suspected of sorcery, he said.

Kepler next set out why it was paramount to distinguish between natural and unnatural illnesses, and went into considerable medical detail to make his statement as authoritative as possible. Its ingenious noting of details that could then be conclusively dismissed [such as inconsistencies in dates or the partiality of witnesses] made this a rhetorical masterpiece. All these magical mystery diseases, Johannes argued, could be explained through medical knowledge and common sense. Johannes did not rule out that sorcery might inflict harm, but said that in these cases the pain was immediate and severe from the start, rather than increasing gradually.

Kepler did indeed believe in magic, yet he tried to use his superior analytical skills to unpick the accusations against his mother. When his mother was finally acquitted he was utterly exhausted and did not correspond with even his closest friends for months. Kepler never published his defence, nor did he try to defend any other woman charged with witchcraft.

This trial reveals that the victims of Germany’s witch craze were not just women. In a society in which reputation mattered so much, each accusation implicated those the woman was related to and had raised. Children might respond with loyalty and love or hatred, repudiation, insecurity or guilt, and these feelings were likely to be mixed and change as cases evolved. Indeed, every member of the Kepler family, including two further siblings, reacted differently to their mother and to the strain of the charges against her. These were experiences shared by hundreds of thousands of Europeans during the witch craze.


Ulinka Rublack is professor of early modern European history at the University of Cambridge and author of The Astronomer and the Witch: Johannes Kepler's Fight for his Mother (Oxford University Press, 2015). To find out more, click here.