Circumference: Eratothenes and the Ancient Quest to Measure the Globe

by Nicholas Nicastro

How do you measure the size of the planet you’re standing on?

Circumference is the story of what happened when one man asked himself that very question. Nicholas Nicastro brings to life one of history's greatest experiments when an ancient Greek named Eratosthenes first accurately determined the distance around the spherical earth. In this fascinating narrative history, Nicastro takes a look at a deceptively simple but stunning achievement made by one man, millennia ago, with only the simplest of materials at his disposal. How was he able to measure the land at a time when distance was more a matter of a shrug and a guess at the time spent on donkey back? How could he be so confident in the assumptions that underlay his that the earth was round and the sun so far away that its rays struck the ground in parallel lines? Was it luck or pure scientific genius? Nicastro brings readers on a trip into a long-vanished world that prefigured modernity in many ways, where neither Eratosthenes' reputation, nor the validity of his method, nor his leadership of the Great Library of Alexandria were enough to convince all his contemporaries about the dimensions of the earth. Eratosthenes' results were debated for centuries until he was ultimately vindicated almost 2000 years later, during the great voyages of exploration. Circumference is a compelling scientific detective story that transports readers back to a time when humans had no idea how big their world was--and the fate of a man who dared to measure the incomprehensible.
“Forget the myth of Columbus' daring in imagining a round earth. Nicastro not only traces the conception of a spherical world back more than a millennium before the seafarer set sail but also recounts in fascinating detail how the ancient Greek geometer Eratosthenes measured that sphere with astonishing accuracy. Though it would be thousands of years before his feat received appropriate recognition, Eratosthenes conducted his revolutionary science with nothing more complex than a sundial and a compass. With reader-friendly clarity, Nicastro explains the surprisingly simple calculations behind the earth measurement. But readers learn about much more than Nicastro delivers the deeply human story of a multitalented genius whose tenure as the head of Alexandria's famed library occasioned remarkable achievements in literature, history, linguistics, and philosophy despite the political turmoil that periodically rocked the Ptolemaic world. Indeed, this polymath plays out his long career against a colorful backdrop peopled with a rich variety of conquerors and cosmologists, murderers and mathematicians. A distant yesterday still furnishes fascinating drama for readers today.”

--Bryce Christensen, Booklist


“Propelled by the story of Eratosthenes's solution of an ancient puzzle -- how big is the earth? -- Circumference offers many unexpected pleasures along the way. With an amiable voice and a flowing style, Nicholas Nicastro brings historical places and people to vivid new life, from the shining city of Alexandria to the great conqueror for whom it was named. A real treat for lovers of history and science.

--Steven Strogatz, author of How Order Emerges from Chaos in the Universe, Nature, and Daily Life, and Schurman Professor of Applied Mathematics, Cornell University

279 pages, Kindle Edition

Published July 21, 2024

About the author

Nicholas Nicastro was born in Astoria, New York in 1963. His education includes a B.A. in English from Cornell University (1985), an M.F.A. in filmmaking from New York University (1991), an M.A. in archaeology and a Ph.D in psychology from Cornell (1996 and 2003). He has also worked as a film critic, a hospital orderly, a newspaper reporter, a library archivist, a college lecturer in anthropology and psychology, an animal behaviorist, and an advertising salesman. His writings include short fiction, travel and science articles in such publications as "The New York Times", "The New York Observer", "Film Comment", and "The International Herald Tribune". His books have been published by Penguin, St. Martin's, and HarperCollins.