Dating Diophantus is no simple matter.
For one thing, the only mathematician he refers to anywhere in his work—specifically, in his On Polygonal Numbers—is Hypsicles of Alexandria.
Born in 190 BC and the author of The Rising of the Zodiacal Signs, Hypsicles is the father of astrology. Hence his interest in the number 12, and the fact that he is also the purported author of Book XIV of Euclid's Elements, on the dodecahedron and icosahedron.
For another, the Suda, a Greek encyclopedia from the 10th century, credits Hypatia of Alexandria with a commentary on Diophantus's Arithmetica. Parts of it may have survived by becoming incorporated into the original text that has come down to us. Murdered by Christian fanatics in 415, Hypatia is the first female mathematician whose life is documented. Furthermore, the Palatine Anthology attributes to Metrodorus of Byzantium—a Greek philosopher of Persian origin who stayed in India in the early 4th century—the epigram from which Diophantus's supposed age at death, 84, can be deduced.
Ultimately, the only reliable dates leave a six-century window of uncertainty. Most historians favor the 3rd century AD. Diophantus may have known Saint Dionysius the Great of Alexandria, who is thought to be the Dionysius to whom he dedicated his Arithmetica. Conversely, Anatolius of Alexandria, Bishop of Laodicea in Syria (the country from which Diophantus may have originated), dedicated to him the ecclesiastical computus used by the Christian Churches. If the date of Easter could be calculated from the year so early on, it may well have been thanks to Diophantus!
