Johannes de Sacrobosco: A Cuckoo In The Nest

One of the more curious characters to emerge from the mire of medieval manuscripts is a monastic scholar with a severe identity crisis: Johannes de Sacrobosco.

Johannes de Sacrobosco, also written Ioannis de Sacro Bosco (c. 1195 – c. 1256), was a scholar, monk and astronomer who was a teacher at the University of Paris.

Giovanni SacroboscoSacroboscoJohn of Holywood

John of Holybush

Jean de Halifax

When it comes to the life and times of Sacrobosco the only things that really stack up are the manuscripts and his numerous aliases.

There is a widespread belief Sacrobosco taught at the University of Paris [aka Sorbonne].

When in 1297 Bartholomaeus de Parma wrote his great commentary on S he stated: “John of Sacrobosco said in his treatise on the Sphere which he composed while he lived in the University of Paris…”, and we have no reason to doubt that this is correct…

In Quest of Sacrobosco – Olaf Pedersen
Journal for the History of Astronomy – Vol 16 No 3 – Oct 1985….16..175P

But everything else is inference, guesswork, speculation, invention and clairvoyancy.

Very little is known about the education and biography of Sacrobosco.

For one thing, his year of death has been guessed at 1236, 1244 and 1256, each with plausibility and each with lack of adequate evidence.

The country in which he was born is uncertain.

Reliable information about the life of Johannes de Sacrobosco is scarce, and standard sources such as the Dictionary of Scientific Biography have unfortunately included as fact material deriving from the speculations and inventions of sixteenth- and seventeenth-century antiquarians.

Starry Messenger – Johannes de Sacrobosco
Department of History and Philosophy of Science of the University of Cambridge.

Nevertheless, the name Sacrobosco does not appear in university records or other historical documents from his own time.

In Quest of Sacrobosco – Olaf Pedersen
Journal for the History of Astronomy – Vol 16 No 3 – Oct 1985

Fittingly, the storyline of Sacrobosco’s first manuscript doesn’t really stack up.

Sacrobosco’s Algorismus aka De Arte Numerandi is thought to have been his first work, and the date is estimated at about 1225, and before 1230.

It’s said this 1225 manuscript introduced Hindu-Arabic numerals into European universities.

Sacrobosco’s Algorismus was the first text to introduce Hindu–Arabic numerals and procedures into the European university curriculum.

In his Tractatus de algorismo , which was used as a textbook until the 16th century, Sacrobosco revealed the basics of arithmetic with integers ranging from the basic arithmetic to the root extraction and was the first to develop a multiplication table based on ten natural numbers.

More commonly it was called Algorismus vulgaris.
Nothing in the text indicates where or when it was written.

In Quest of Sacrobosco – Olaf Pedersen
Journal for the History of Astronomy – Vol 16 No 3 – Oct 1985

Evidently, this wasn’t a very successful introduction because it took another 300 years for the format of the numerals to stabilise and spread to business and schools.

Just as we were quite uncertain as to the origin of the numeral forms, so too are we uncertain as to the time and place of their introduction into Europe.

The question is often asked, why did not these new numerals attract more immediate attention ?

Why did they have to wait until the sixteenth century to be generally used in business and in the schools ?

The Hindu-Arabic Numerals
David Eugene Smith and Louis Charles Karpinski – 1911

The second Sacrobosco script was so spectacularly successful it became [so we are told] a “compulsory” textbook for an astounding 400 years in the strangely static sphere of academia.

About 1230, his best-known work, Tractatus de Sphaera (On the Sphere of the World) was published.

In this book, Sacrobosco gives a readable account of the Ptolemaic universe.

Ptolemy’s (updated) Almagest had been translated into Latin in 1175 by Gerard of Cremona from the Arabic translation held in Toledo and copies had quickly found their way to Paris.

The Sphere was required reading by students in all Western European universities for the next four centuries.

Johannes de Sacrobosco discusses the place of the earth in the universe , the spherical shape of the earth, including the earth measurement, the climatic zones of the earth, the emergence of the eclipses, etc.

This work circulated before the invention of book printing in manuscripts, first appeared in 1472 in print and was up to 1650 printed in about 240 editions.

It was used throughout Europe as a compulsory elementary textbook of astronomy until well into the 17th century.

In the grand scheme of things this second Sacrobosco script is said to demonstrate 13th century Christianity was spherically enlightened and very far removed from the primitive Flat Earth beliefs of earlier times.

Cosmas Indicopleustes was a Greek merchant and later hermit from Alexandria of Egypt. He was a 6th-century traveller, who made several voyages to India during the reign of emperor Justinian.

Christian Topography
A major feature of his Topographia is Cosmas’ worldview that the world is flat, and that the heavens form the shape of a box with a curved lid.

He was scornful of Ptolemy and others who held that the world was spherical.

Cosmas aimed to prove that pre-Christian geographers had been wrong in asserting that the earth was spherical and that it was in fact modelled on the tabernacle, the house of worship described to Moses by God during the Jewish Exodus from Egypt.

Three nearly complete manuscripts are known to exist. The earliest and best is from the 9th century, and is in the Vatican Library. This text has only ten books. Two closely related manuscripts of the 11th century

But the strictly biblical men of science, such eminent fathers and bishops as Theophilus of Antioch in the second century, and Clement of Alexandria in the third, with others in centuries following, were not content with merely opposing what they stigmatized as an old heathen theory ; they drew from their Bibles a new Christian theory, to which one Church authority added one idea and another another, until it was fully developed.

Taking the survival of various early traditions, given in the seventh verse of the first chapter of Genesis, they insisted on the clear declarations of Scripture that the earth was, at creation, arched over with a solid vault, ” a firmament,” and to this they added the passages from Isaiah and the Psalms, in which it declared that the heavens are stretched out ” like a curtain,” and again ” like a tent to dwell in.”

The universe, then, is like a house : the earth is its ground floor, the firmament its ceiling, under which the Almighty hangs out the sun to rule the day and the moon and stars to rule the night.

This ceiling is also the floor of the apartment above, and in this is a cistern, shaped, as one of the authorities says, ” like a bathing-tank,” and containing ” the waters which are above the firmament.”

These waters are let down upon the earth by the Almighty and his angels through the ” windows of heaven.”

As to the movement of the sun, there was a citation of various passages in Genesis, mixed with metaphysics in various proportions, and this was thought to give ample proofs from the Bible that the earth could not be a sphere.

A History of The Warfare of Science with Theology in Christendom – Volume 1
Andrew Dickson White – 1896

Again, the supporting evidence doesn’t really stack up as Flat Earth Christianity managed to linger on for another 300 years.

Many a bold navigator, who was quite ready to brave pirates and tempests, trembled at the thought of tumbling with his ship into one of the openings into hell which a widespread belief placed in the Atlantic at some unknown distance from Europe.

This terror among sailors was one of the main obstacles in the great voyage of Columbus.

In a mediaeval text-book, giving science the form of a dialogue, occur the following question and answer:

” Why is the sun so red in the evening ? ”
” Because he looketh down upon hell.”

But the ancient germ of scientific truth in geography – the idea of the earth’s sphericity – still lived.

Although the great majority of the early fathers of the Church, and especially Lactantius, had sought to crush it beneath the utterances attributed to Isaiah, David, and St. Paul, the better opinion of Eudoxus and Aristotle could not be forgotten.

Clement of Alexandria and Origen had even supported it.

Ambrose and Augustine had tolerated it, and, after Cosmas had held sway a hundred years, it received new life from a great churchman of southern Europe, Isidore of Seville, who, however fettered by the dominant theology in many other things, braved it in this.

In the eighth century a similar declaration was made in the north of Europe by another great Church authority, Bede.

Against the new life thus given to the old truth, the sacred theory struggled long and vigorously but in vain.

Eminent authorities in later ages, like Albert the Great, St. Thomas Aquinas, Dante, and Vincent of Beauvais, felt obliged to accept the doctrine of the earth’s sphericity, and as we approach the modern period we find its truth acknowledged by the vast majority of thinking men.

The Reformation did not at first yield fully to this better theory.

Luther, Melanchthon, and Calvin were very strict in their adherence to the exact letter of Scripture.

Even Zwingli, broad as his views generally were, was closely bound down in this matter, and held to the opinion of the fathers that a great firmament, or floor, separated the heavens from the earth; that above it were the waters and angels, and below it the earth and man.

The main scope given to independent thought on this general subject among the Reformers was in a few minor speculations regarding the universe which encompassed Eden, the exact character of the conversation of the serpent with Eve, and the like.

In the times immediately following the Reformation matters were even worse.

The interpretations of Scripture by Luther and Calvin became as sacred to their followers as the Scripture itself.

When Calixt ventured, in interpreting the Psalms, to question the accepted belief that ” the waters above the heavens ” were contained in a vast receptacle upheld by a solid vault, he was bitterly denounced as heretical.

In the latter part of the sixteenth century Musasus interpreted the accounts in Genesis to mean that first God made the heavens for the roof or vault, and left it there on high swinging until three days later he put the earth under it.

But the new scientific thought as to the earth’s form had gained the day.

The most sturdy believers were obliged to adjust their biblical theories to it as best they could.

A History of The Warfare of Science with Theology in Christendom – Volume 1
Andrew Dickson White – 1896

The third manuscript of 1235 is where the Sacrobosco saga becomes seriously suspect.

What Sacrobosco may be most famous for is his criticism of the Julian calendar.

In his book on computus, entitled in Latin De Anni Ratione (English: On reckoning the years), dated circa 1235, he maintained that the Julian calendar had accumulated an error of ten days and that some correction was needed.

The imprecise 365.25 days had resulted in an accumulated error of about 10 days by the 13th century. Sacrobosco made no proposal on how to get rid of the accumulated error.

But looking to the future, he proposed to leave one day out of the calendar every 288 years to prevent continuing error.


The Sacrobosco manuscript of 1235 AD that famously criticised the Julian calendar [very coincidentally] appeared the year after the first dated coin was minted in Europe during 1234 AD.

One of the peculiarities of this storyline is that dated coins did not become prevalent in Europe for another 300 years.


Similarly, Sacrobosco’s manuscript of 1235 AD was 300 years ahead of it’s time.

Between 1531 and 1673 this Sacrobosco text appeared in [at least] 35 printed editions.

Sacrobosco’s dependence upon other writers on the calendar, in particular on both Robert Grosseteste (c. 1170-1253) and the unknown author of a more elementary Compotus, is a matter of some dispute.

It is worth noting, however, that Sacrobosco’s Compotus [aka De Anni Ratione] was one of the medieval calendrical treatises popular at the time of the Gregorian Reform: it went through at least 35 editions between 1531 and 1673, many of them at Wittenberg, where it was promoted by the reformer Philipp Melanchthon.

Starry Messenger – Sacrobosco and Calendar Reform
Department of History and Philosophy of Science of the University of Cambridge.


The dating of Sacrobosco’s third manuscript to 1235 AD is based solely upon his clairvoyant claim that 65 cycles of 19 solar years had occurred since the Incarnation.

He begins by stating that “According to Ptolemy in Book III of the Almagest 19 solar years are equals to 6039 days 18 hours although by a very crude computation.

Sacrobosco continues by saying that “according to Book IV of the Almagest the lunar cyclus decemnovennalis of 235 lunations is 6939 days 16 hours and nearly 2/3 hours”.

The difference is 1 + 1/3 of an hour, and Sacrobosco maintains that this amounts to 65 hours + 65/3 hours over the time which have elapsed since the Incarnation.

This implies that this period of time equals 65 complete cycles of 19 years each.

Therefore we must have N = 65 x 19 = 1235.

In Quest of Sacrobosco – Olaf Pedersen
Journal for the History of Astronomy – Vol 16 No 3 – Oct 1985

This claimed date is the basis for guesstimating other dates in the Sacrobosco saga.


The mainstream is rather pleased Sacrobosco identified an accumulated error of 10 days in the Julian Calendar about 300 years before Pope Paul II was authorised to reform the calendar.

In his book on computus, entitled in Latin De Anni Ratione (English: On reckoning the years), dated circa 1235, he maintained that the Julian calendar had accumulated an error of ten days and that some correction was needed.

In 1545, the Council of Trent authorized Pope Paul III to reform the calendar, requiring that the date of the vernal equinox be restored to that which it held at the time of the First Council of Nicaea in 325 and that an alteration to the calendar be designed to prevent future drift.

When the new calendar was put in use, the error accumulated in the 13 centuries since the Council of Nicaea was corrected by a deletion of 10 days.

The Julian calendar day Thursday, 4 October 1582 was followed by the first day of the Gregorian calendar, Friday, 15 October 1582 (the cycle of weekdays was not affected).

However, this joy is misplaced because Sacrobosco’s contradicts the 1235 AD dating and 10 day calendar drift when he proposes leaving one day out of the calendar every 288 years.

Sacrobosco made no proposal on how to get rid of the accumulated error.

But looking to the future, he proposed to leave one day out of the calendar every 288 years to prevent continuing error.

The problems being that:

a) Between the implementation of the Julian Calendar in 45 BC and the claimed date of 1235 AD the calendar drift of 1 day in every 288 years would amount to only 4 days [in whole numbers]
i.e. (45 + 1235) / 288 = 4.444

b) It takes 2,880 years to accumulate 10 days at the rate of 1 days every 288 years.
i.e. long after Sacrobosco’s [final] bedtime.

Given the contradictory mathematics it’s miraculous the mainstream is still marketing this shabby Sacrobosco saga as a genuine product of the 13th century.

Arguably, Sacrobosco was not a person but a marketing franchise that was active for about a century i.e. the difference between appearing 300 and 400 years out of context.

Either way:

The evidence suggests the biography of Sacrobosco has [at some point] been deliberately backdated by about 300 years to provide the illusion the Gregorian Calendar Reforms can be explained away by long standing academic arguments that authoritatively identified a very small calendar drift that very gradually accumulated in the centuries after the Incarnation.



Who controls the past controls the future.
Who controls the present controls the past.

George Orwell

In other words:

Settled Science has a long and shabby provenance that’s very venerable.

Gallery | This entry was posted in Books, Heinsohn Horizon, History, Inventions and Deceptions, Science, Uniformitarianism. Bookmark the permalink.

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