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**Aristaeus the Elder** (Greek: Ἀρισταῖος ὁ Πρεσβύτερος; 370 – 300 BC) was a Greek mathematician who worked on conic sections. He was a contemporary of Euclid.

Only little is known of his life. The mathematician Pappus of Alexandria refers to him as Aristaeus the Elder. Pappus gave Aristaeus great credit for a work entitled *Five Books concerning Solid Loci* which was used by Pappus but has been lost. He may have also authored the book *Concerning the Comparison of Five Regular Solids*. This book has also been lost; we know of it through a reference by the Greek mathematician Hypsicles.

Heath 1921 notes, "Hypsicles (who lived in Alexandria) says also that Aristaeus, in a work entitled *Comparison of the five figures*, proved that the same circle circumscribes both the pentagon of the dodecahedron and the triangle of the icosahedron inscribed in the same sphere; whether this Aristaeus is the same as the Aristaeus of the Solid Loci, the elder contemporary of Euclid, we do not know."^{[1]}