Medieval calculations

Recognising the difficulty of following an algorithm in prose using Latin numerals, some medieval scribes highlighted the numerals in red ink. From Boethius’ De institutione arithmetica, one of the medieval ‘textbooks’ on algebra. Paris, Bibliothèque nationale de France, Latin 10251.

There are many sad truths about medieval manuscripts. They took extremely long to write. Scribes’ eyesight was a common casualty of book-copying. The books themselves were fragile objects, targets of depradations, subject to damage and destruction.

But in the Latin west, there was nothing more sad than the effort of medieval scholars and mathematically-minded writers to conduct algebric calculations using Roman numerals. My heart goes out to all those scribes who, keen to demonstrate a mathematical truth or share an astronomical insight, struggled to combine bars, V’s, X’s, C’s, L’s, D’s and M’s on the jumbled manuscript page. With Arabic numerals unbeknownst to them, early medieval scholars filled parchment leaf after parchment leaf with arcane formulas that even a modern reader finds hard, if not impossible, to follow.

Perhaps the most complicated algaebric mission in the medieval West was that related to establishing the moveable date of Easter. During the 9th, 10th and 11th centuries, Western intellectuals came up with increasingly more sophisticated ways of calculating astronomical ephemera on the basis of mathematical formulas and the observation of the Sun, the Moon and a couple of other planets visible to the naked eye. Before the arrival of Arabic numerals in the West around the end of the 11th century, all such calculations were conducted in Latin ‘code’. And it was a frightfully difficult task. But the monks didn’t give up. Computus, the science of achieving calendrical precision, kept math alive through troubled centuries.

Pursuing Latin-numeral-based algorithms is the cruelest form of arithmetical torture. But the West came out of it stronger. And modern science and mathematics owe their continued existence to the countless scribes who computed and speculated in painstaking lines of freakish code, letterforms parading as numerals.

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