Dionysodorus of Amasia

Dionysodorus of Amisene (1st century AD) was a Greek mathematician from Pontus, now on the Black Sea coast of Turkey. He was briefly described by Strabo, as one of the learned men of the city of Amisus. whom Pliny the Elder describes as having calculated the circumference of the Earth, less accurately than the older calculation of Eratosthenes. He should also be distinguished from Dionysodorus of Caunus, who studied conic sections.

Dionysodorus of Amisene was long thought to be the Dionysodorus who studied conic sections until, in the early 20th century, found from a papyrus newly excavated at Herculaneum a connection from the study of conics to Dionysodorus of Caunus and his son, also named Dionysodorus, dating them to centuries before the time that Strabo wrote about.