L. Sprague de Camp’s Lest Darkness Fall first saw light as a short story in the December 1939 issue of Unknown magazine before being expanded into a full novel for hardcover publication by Henry Holt & Company in 1941. Unknown was the companion magazine to Astounding, both of which were edited by John W. Campbell, the godfather of the “Golden Age of Science Fiction”. Campbell had taken the reins of Astounding in 1937 and had almost immediately turned it away from its freewheeling high adventure origins towards more scientifically plausible and therefore “realistic” stories. In 1939, Campbell launched Unknown with a very similar mandate towards fantasy fiction; his direction to writers was “For Astounding I want stories which are good and logical and possible. For Unknown, I want stories which are good and logical.”

As an aeronautical engineer by training and a paleontologist, historian and educator by inclination, L. Sprague de Camp was an exemplar of the new breed of scientifically savvy writer that Campbell was cultivating. De Camp’s essentially rationalist worldview seems to have given him trouble in depicting the truly impossible, at least in his nominally science fiction works. It makes sense then that he’d quickly gloss over the mechanics and metaphysics of time travel in Lest Darkness Fall in favor of playing to his strengths, in this case a deep knowledge of Late Antiquity, specifically the Gothic War (535-554) that devastated the Italian peninsula and sent it into a state of decline that was only reversed with the coming of the Italian Renaissance.

Lest Darkness Fall was de Camp’s first solo novel, but even then some of his tropes were in evidence, such as the highly educated and rational protagonist making his way in a strange new world, both aided and opposed by often comical or even buffoonish locals. De Camp’s writing can be compromised at times by the feeling that he’s holding himself above the material or at least failing to fully embrace it, but thankfully that’s not the case with Lest Darkness Fall. Padway’s dry wit rarely devolves into snark, and his 20th century education and native intelligence aren’t always enough to carry the day–ultimately Padway relies on persuasion as much as intellect.

Lest Darkness Fall’s balance of well-developed characters and careful extrapolation of history made it a cornerstone of the Alternate history sub-genre of fantastic fiction to this day as witnessed by its frequent reprintings over the last 80 years. It has also drawn reponses in the form of the short stories “The Man Who Came Early” (1956) by Poul Anderson, “The Deadly Mission of Phineas Snodgrass” (1962) by Frederik Pohl, “To Bring the Light” (1996) by David Drake, and “The Apotheosis of Martin Padway” (2005) by S.M. Stirling. The current king of alternate history fiction Harry Turtledove recently tweeted that the book changed his life: “ L. Sprague de Camp’s LEST DARKNESS FALL. Without It, I wouldn’t have studied Byzantium, and my whole life would be, well, an alternate history.”