Quick answer: Guido Bonatti, c.1207 to c.1296, was the most famous astrologer of 13th-century Italy. His vast encyclopedia, the Liber Astronomiae (Book of Astronomy, c.1277), organised the whole art and synthesised Arabic, Greek and Latin sources. He served Italian lords as a court astrologer, and Dante later placed him in the Inferno among the diviners.
Few figures in the history of astrology loom as large as Guido Bonatti of Forli. In an age when astrology stood close to the centre of learning and politics, he was widely regarded as the foremost astrologer of his time. His great book gathered the scattered traditions of the art into one ordered whole, and his reputation was so vivid that it survived in poetry long after his death.
Who Guido Bonatti was
Guido Bonatti lived from about 1207 to about 1296 and came from Forli, a city in Italy. By the standards of his century he was a celebrity, often described as the most famous astrologer of the 13th century and sometimes as the foremost astrologer of his age.
He worked as a practising astrologer in the service of several Italian lords, not as a distant theorist but as an adviser whose judgements bore directly on events. This combination of learning and public influence gave his name a weight that few of his contemporaries could match.
Astrologer to the lords of Italy
Bonatti served as court astrologer to several Italian rulers, most famously Guido da Montefeltro at Forli. In that role he advised on matters of state and on the timing of action, helping his patrons decide when to move and when to wait.
The most celebrated story attached to him concerns the defence of Forli against papal forces in 1282. He is reported to have astrologically timed a sortie during the siege, after which the city won the engagement. The episode was remembered in later portraits of him and helped fix his image as an astrologer whose counsel shaped real campaigns.
The Liber Astronomiae
His major work is the Liber Astronomiae, the Book of Astronomy, written around 1277. It is a vast and systematic encyclopedia that set out to organise the entire art of astrology in a single, ordered reference.
What makes the book remarkable is its synthesis. Bonatti drew together Arabic sources such as Abu Ma'shar, al-Kindi and Messahala, Greek authority above all Ptolemy, and the Latin tradition that had grown up in the West. From these strands he wove a coherent and practical whole, presenting not just isolated rules but a working system a reader could actually follow.
What the book covers
The Liber Astronomiae addresses the full sweep of medieval practice. It treats nativities, the reading of birth charts; elections, the choosing of favourable times to begin an undertaking; horary astrology, the answering of a specific question from a chart cast for the moment it is asked; and mundane astrology, concerned with the world at large and with weather.
This completeness is exactly why the book mattered. It became a standard reference for centuries and was printed in 1491 and again in 1550, long after manuscript copies first circulated. A reader can still trace in it one of the most complete pictures we have of high-medieval astrological method. If you would like to see a birth chart of the kind the nativity sections describe, you can cast a free birth chart and read the same houses and planets Bonatti worked with.
Dante and a lasting legacy
Such was Bonatti's fame that Dante placed him in the Inferno among the diviners. The choice cuts two ways. It marks both his celebrity, since only a well-known figure would be recognised by readers, and the Church's disapproval of divination, which Dante reflected by setting the soothsayers in a sorrowful place.
The legacy outlived the controversy. Because the Liber Astronomiae preserved so much of the older Arabic and Greek inheritance in usable form, it remains an important source for the modern revival of traditional and horary astrology. For more on the people and ideas behind the craft, you can browse the blog.
Frequently Asked Questions
Who was Guido Bonatti?
Guido Bonatti, who lived from about 1207 to about 1296, was an astrologer from Forli in Italy. He was the most famous astrologer of the 13th century and served as court astrologer to several Italian lords, most famously Guido da Montefeltro.
What is the Liber Astronomiae?
The Liber Astronomiae, or Book of Astronomy, is Bonatti's major work, written around 1277. It is a vast and systematic encyclopedia that synthesised Arabic, Greek and Latin sources and covered nativities, elections, horary and mundane astrology. It became a standard reference for centuries and was printed in 1491 and 1550.
Why did Dante put Bonatti in the Inferno?
Dante placed Bonatti among the diviners in the Inferno because divination was disapproved of by the Church. The choice also shows how famous Bonatti had become, since Dante expected his readers to recognise the name.
