Dionysodorus of Amaseia

Dionysodorus of Amaseia (Διονυσόδωρος ο Αμασιεύς, 1st century AD) was a Greek mathematician from Amaseia in Pontus.

Pliny the Elder, who lived during the same era, mentions that Dionysodorus calculated the circumference of the Earth and found it to be 42,000 stadia - a value significantly different from the larger and more accurate measurement of Eratosthenes in the 3rd century BC, which was 252,000 stadia, regardless of the value of the stadium used. There is often confusion between Dionysodorus of Amaseia and Dionysodorus of Caunus, who studied conic sections.