Histories of computing tend to either begin with ancient efforts — like the abacus, Archimedes’ mechanical theorems, and Aristotle’s logic — or they skip ahead to the early modern period, recounting stories of Gottfried Leibniz’s calculating machine, Charles Babbage’s Difference Engine, or Ada Lovelace’s recursive algorithm. That is, if they haven’t jumped straight ahead to the work of the Claude Shannons, Konrad Zuses, and Alan Turings of the 20th century. Rather neglected in this story are the parts in between: the weird and wonderful contributions of the Middle Ages. As I’ve written elsewhere, the Dark Ages weren’t all that dark, and this period of intellectual history is rather hard done by. To remedy this shortcoming, here are four computation systems from the Middle Ages you have (probably) never heard of.