*Euclides ab omni naevo vindicatus* (1733), or *Euclid Vindicated of All Errors*, was a logical study of the structure of Euclid’s geometry with an emphasis on the place of the Parallel Postulate. Its author Girolamo Saccheri (1667-1733) was a Jesuit logician. Using the technique of *reductio ad absurdum*, his findings opened the possibility of the existence of other geometries.

This is the Preface for *Euclides,* in which Saccheri explained his work.

This is the first page of text for *Euclid Vindicated of All Errors*.

*These images from its George Arthur Plimpton Collection are presented through the courtesy of the Columbia University Libraries.*

Index to Mathematical Treasures