What inspired you to write The Abacus and the Cross?

I was introduced to The Scientist Pope through an act of grace. Writing my previous book, The Far Traveler, about an adventurous Viking woman, I found myself making an imaginary pilgrimage to Rome just after the year 1000. Wondering which pope (if any) Gudrid the Far-Traveler had met, I discovered Gerbert of Aurillac, Pope Sylvester II.

I was astonished. Nothing in my many years of reading about the Middle Ages had led me to suspect that the pope in the year 1000 was the leading mathematician and astronomer of his day.

Nor was his science just a sidelight. According to a chronicler who knew him, he rose from humble beginnings to the highest office in the Christian Church “on account of his scientific knowledge.”

To my mind, scientific knowledge and medieval Christianity had nothing in common. I was wrong.

I felt as if I had stumbled into a parallel universe, an alternate history of the Middle Ages that had been perfectly crafted for me: For most of my career, I have worked as a science writer, but my heart had first been captured by medieval sagas. The story of The Scientist Pope—one scholar called him “the Bill Gates of the end of the first millennium”—was a story I needed to tell.

It didn’t hurt that from about 70 years after his death in 1003 until today he was known (if at all) not as a scientist, but as a wizard—a sorcerer who had sold his soul to the devil. According to a thirteenth-century writer, he was “the best necromancer in France, whom the demons of the air readily obeyed in all that he required of them by day and by night.”

This legend inspired fantasy writer Judith Tarr to include Gerbert as a magical character in two of her novels, Ars Magica and The Eagle’s Daughter, both of which I loved.

But I found the truth about Gerbert’s life, once I unearthed it, even more fascinating.

A professor at a cathedral school for most of his career, Gerbert of Aurillac was the first Christian known to teach math using the nine Arabic numerals and zero. He devised an abacus, or counting board, that mimics the algorithms we use today for adding, subtracting, multiplying, and dividing. It has been called the first counting device in Europe to function digitally—even the first computer. In a chronology of computer history, Gerbert’s abacus is one of only four innovations mentioned between 3000 BC and the invention of the slide rule in 1622.

Like a modern scientist, Gerbert questioned authority. He experimented. To learn which of two rules best calculated the area of an equilateral triangle, he cut out square inches of parchment and measured the triangle with them. To learn why organ pipes do not behave acoustically like strings, he built models and devised an equation. (A modern physicist who checked his result calls it ingenious, if labor-intensive.)

Gerbert made sighting tubes to observe the stars and constructed globes on which their positions were recorded relative to lines of celestial longitude and latitude. He (or more likely his best student) wrote a book on the astrolabe, an instrument for telling time and making measurements by the sun or stars. You could even use it to calculate the circumference of the earth, which Gerbert and his peers knew very well was not flat like a disc but round as an apple.

Much of this science Gerbert learned as a youth living on the border of Islamic Spain, then an extraordinarily tolerant culture in which learning was prized. Born a peasant in the mountains of France in the mid-900s, Gerbert entered the Benedictine monastery at Aurillac as a boy. He learned to read and write in Latin. He studied Cicero, Virgil, and other classics. He impressed his teacher with his skill in debating. He was a fine writer, too, with a sophisticated style graced with rhetorical flourishes. To further his education, his abbot sent him south to Christian Barcelona, which then had diplomatic ties with the Islamic caliphate of al-Andalus.

In the caliph’s library in Cordoba were at least 40,000 books (some said as many 400,000); Gerbert’s French monastery owned less than 400. Many of the caliph’s books came from Baghdad, known for its House of Wisdom, where for 200 years works of mathematics, astronomy, physics, and medicine had been translated from Greek and Persian and Hindu and further developed by Islamic scholars under their caliph’s patronage. In the world Gerbert knew, Arabic was the language of science. During his lifetime, the first Arabic science books were translated into Latin through the combined efforts of Muslim, Jewish, and Christian scholars.

Science was of such importance, I was surprised to learn, that these scholars were willing to overlook all their religious and political differences. Christian, Muslim, or Jewish, Arab or French, Saxon or Greek, they sat down together to translate books, to make scientific instruments, and to further their understanding of mathematics, astronomy, and logic. Many of these scholars were churchmen, and some became Gerbert’s lifelong friends.

The story of Gerbert of Aurillac made me realize that the major conflicts in our world today, between Christianity and Islam, between religion and science, are not inevitable and inescapable.

His story taught me that a world based on peace, tolerance, law, and the love of learning was not a fantasy world—not an alternate universe after all. For a short period of time around the year 1000, it did exist.

In the course of my quest to discover The Scientist Pope, I visited the cathedral of Saint John the Lateran in Rome, where his marble tombstone now hangs on a pillar in the right aisle. Pope Sergius IV, who had been Gerbert’s papal librarian, wrote his epitaph. It reads, in part: “The emperor, Otto III, to whom he was always faithful and devoted, loved him greatly and offered him this church of Rome. They illuminated their time, emperor and pope, by the brilliance of their wisdom. The century rejoiced.” Upon Gerbert’s death, Sergius said, “the world was darkened and peace disappeared.”

How prophetic those words, written in 1009, now sound. Less than a hundred years later, a pope would launch the first Crusade, and The Scientist Pope would be branded a sorcerer and devil-worshipper for having taught the science that had come into Christian Europe from Islamic Spain.

What’s the most important take-home message for readers?

The popular picture of the Dark Ages is wrong. The earth wasn’t flat. People weren’t terrified that the world would end at midnight on December 31, 999. Christians did not believe Muslims and Jews were the enemy. The Church wasn’t anti-science.

In the Dark Ages, contrary to what most people think, science was central to the lives of monks, kings, emperors, and even popes. It was the mark of true nobility and the highest form of worship of God.

Is there anything you had to leave out?

A marvelous side effect of writing a book like this one that is outside my comfort zone of knowledge was that I had to ask for help. I found it in Barcelona, Paris, Frankfurt, Munich, Monistrol-sur-Loire, London, Fribourg, Bobbio, New Haven, and Rome, where I was fortunate to spend time with several of the modern scholars who are bringing Gerbert’s life and accomplishments to light. I am very grateful for their generosity in teaching me what I needed to know.

They combine extraordinary talents. It is difficult to track Gerbert’s ideas, I learned, unless you know both Arabic and Latin, mathematics, logic, astronomy, Church history, and, of course, paleography, for much of Gerbert’s work and that of his peers has never been published and exists only in manuscripts (or scraps of manuscripts). It helps to be a tinkerer, who can reconstruct a scientific instrument from a mere hint on how it works, and a puzzler who likes playing with acrostics and chronograms.

A knowledge of astrology, David Juste of the University of Sydney, Australia, assured me, was crucial. To convince me, he met me in Paris and showed me a manuscript, an incident I will never forget. We were in the manuscript reading room of the National Library of France, a bright, hushed room, floor-to-ceiling bookcases to my left, floor-to-ceiling windows to my right, ranks of long tables studded with wooden bookrests and velvet rolls to gently prop open the fragile parchment pages. Most of the chairs were filled with hunched-over scholars.

To be admitted, I had to write ahead and state my credentials, submit to an interview, show my passport, prove myself a “scholar” by handing over a letter from my publisher, be photographed (at another desk), get a plastic ID card, go down to the cashier and pay seven euros for the card to be activated for three days and to get three paper tickets. Up to the manuscript room, where I handed the ID card and one ticket to the clerk. She gave me a key to a locker, where I had to leave all my belongings except one pencil (not a pen, with which I could deface a manuscript) and a notebook. Reentering the reading room, I had to display my pencil and notebook to the clerk to get back my ID card and the ultimate prize: a plastic block with a number on it. I was then permitted to sit in a chair—but not look at any manuscripts, yet.

Juste sat down beside me. “What you will see here,” he whispered, “is the earliest Latin manuscript to contain Arabic words. The earliest proof of the transmission of Arabic science to the West. Now I will order the manuscript.”

He filled out a form and took it to another desk.

Ten minutes later, the manuscript arrived from the vault. It was a rather thin little book, with a newish leather binding. The parchment was off-white with brown letters, undistinguished. He turned the page, did the classic French kissing of the finger tips: “This is it.”

It was made in Limoges, France, sometime between 978 and 1000. It was a book on astrology—fortune-telling: how to predict the outcome of an illness, the character of a child, the success of a journey or a marriage or a battle, the site of buried treasure, the identity of a thief. Fifteen chapters tell how to forecast the weather.

Juste looked around nervously. “Wait a minute. We have to be very careful. I expect we’ll get in trouble. We are not supposed to consult the manuscripts together. Why? It’s the rules. The rules are very strict. I have an idea.” He got up. “I’ll try something.” He intercepted a different clerk, a young woman who had just come from a back room. She studied me, then curtly nodded. He hurried back and swept up the manuscript.

“This way. I asked for special permission to talk.” We went into the back room, where a trio who looked like professor and students were discussing another manuscript. We sat down at the opposite end of the long table; the clerk closed the door.

Juste relaxed. He began flipping through the pages, pointing to letters, running his finger along a line, thumbing pages back and forth—for all the hoopla, he didn’t treat “the earliest proof of the transmission of Arabic science to the West” as a sacred object. It was a book.

What are some of the biggest misconceptions about your topic?

Most books about the Dark Ages skip the science, implying medieval people had no interest in it. Books that do address medieval science are often dense and technical, written by experts for experts. They focus too closely on one subject—the history of geometry, the history of the astrolabe—failing to give the broader picture of a vibrant scientific curiosity.

Even these books usually overlook Gerbert’s era (950-1003), jumping from Charlemagne’s school reforms in the 800s to the first full Latin translation of Euclid’s Elements in the mid-1100s, for the good reason that the manuscripts and instruments attesting to Gerbert’s accomplishments as a scientist and teacher have only been identified in the last 10 years. News of them has not passed beyond the smallest of academic circles; most discoveries have not been published in English.

Most books on the Dark Ages tell of war, famine, and plague; of Viking raids and Saracen atrocities; of the origins of the Crusades; and of the rising concepts of feudalism and chivalry. They focus on one language or one nation or one empire. By looking instead at one man—whose life spanned many empires, nations, and languages, and who crossed the seeming divides between religion and science, the cloister and the palace—I hope to change readers’ perception of the Dark Ages.

Did you have a specific audience in mind?

I wrote The Abacus and the Cross for everyone interested in the Middle Ages or the history of science. But my secret hope is that fantasy writers like Judith Tarr and Kate Elliott will use it as a source in their future novels. I’d like to see the Dark Ages become less monolithic in fiction in general. In films, video games, and historical novels you never see a medieval monk who is a true scientist, but there were many of them. Gerbert was not exceptional in that way. He was a typical tenth-century monk, though a more gifted teacher than many.

Are you hoping to just inform readers? Give them pleasure? Piss them off?

A good nonfiction book both informs and entertains. I don’t want to piss anyone off, but perhaps knock them on the head. I want to open their eyes to a world they’ve been missing, the world of science in the Dark Ages.

While working on The Abacus and the Cross, for example, I found this paragraph in a history published in 1999 by a well-known volcanologist:

Scholarly work on the nature of the Earth ceased with the end of the Classical period and the fall of the Roman Empire in the Dark Ages (ca. AD 400 to 1000), and it can be said that with the rise of Christianity, the European continent suffered a scholarly amnesia during the Middle Ages to about AD 1300. Some learning and knowledge of nature inherited from the writers of antiquity survived in monasteries, but little progress was made in philosophical or scientific inquiry—and studies into the nature and origin of the Earth were virtually nonexistent. The impediments imposed by the new religion were many—no opinions were allowed that ran contrary to orthodox beliefs. Scriptural dogma led to a retreat of knowledge on all fronts concerning Earth science, even to a retreat to the concept of a flat Earth.

I’ve asked my publisher to send the author, who has since become a friend of mine, a copy of The Abacus and the Cross. I don’t ever want to read such nonsense in a serious work of history again. No one in the year 1000 thought the earth was flat.

Even the most mystical of the chroniclers of the time, Ralph the Bald, the one who recorded all the signs and wonders presaging the Apocalypse and attributed every act and event to the will of God—even Ralph knew the earth was round. Describing the imperial insignia, he said it was “made in the form of a golden apple set around in a square with all the most precious jewels and surmounted by a golden cross. So it was like this bulky earth, which is reputed to be shaped like a globe.”

What alternative title would you give the book?

The Abacus and the Cross was the first title that came to me, and I wouldn’t change it. It’s short, but broad enough to take in all of Gerbert’s many facets. And it holds within itself the crucial tension of the book, between science and religion.

How do you feel about the cover?

The designer did a brilliant job. The cover evokes just the right balance of wonder and scientific inquiry. And I like having my name up there in the stars.

What book do you wish you had written?

If I could have brought the modern scholarship to life, instead of merely reporting it, I would have. But there are only so many things you can accomplish in one book without it becoming a tome. Gerbert’s own life was complicated enough.

In addition to being a scientist and a teacher, he was a spy, a traitor, a kingmaker, and a visionary.

He and the young emperor Otto III shared a dream. Gerbert encouraged Otto to see himself as a second Charlemagne—one with royal Byzantine blood. Otto could reunite Rome and Constantinople, expanding the Holy Roman Empire (then just parts of Germany and Italy) to recreate the vast unified realm of the Caesars. Otto and Gerbert brought two of the scourges of Europe—the Vikings in the north and the Hungarian Magyars in the east—into the Christian fold. They established the Polish Catholic Church and sent missionaries to the Prussians, Swedes, and other pagan tribes; they strengthened the empire’s ties with Spain and made overtures to Constantinople.

But Otto died in 1002, just twenty-two—and Gerbert a year later, some say of grief. Their plans for a Christian Empire based on peace, tolerance, and the love of learning died with them.

What’s next?

I am beginning a book on the thirteenth-century Icelandic writer Snorri Sturluson.To me, the defining artistic moment of the twentieth century was the publication of J.R.R. Tolkien’s The Hobbit in 1937. From this book and its sequel, The Lord of the Rings in 1954, an entire industry was created—not just fantasy novels, but fantasy films, video games, board games, role-playing games, and online multi-player games.

And yet the ideas that make Tolkien popular—the ideas picked up by his imitators—are not all original. Many are the work of Snorri Sturluson. Without Snorri, modern fantasies would include no tall, beautiful, immortal elves; no evil dark elves or orcs; no dwarves making weapons in their halls of stone; no peaceful farmers who metamorphose at night into bears; no giant eagles who carry men about or people who fly when they don a feather cloak; no riddling dragons; no wandering wizards who talk to birds. The millions of readers and gamers worldwide who enjoy these fantasy elements have no idea they owe a debt of gratitude to medieval Iceland. They have no idea who Snorri Sturluson is. It’s time they learned.