Menelaus of Alexandria (c. 70–130 AD), who wrote a work dealing with the geometry of the sphere and its application to astronomical measurements and calculations (Spherica). Similar examples of applied mathematics include the construction of analogue computers like the Antikythera mechanism, the accurate measurement of the circumference of the Earth by Eratosthenes (276–194 BC), and the mechanical works of Hero (c. 10–70 AD). Several centers of learning appeared during the Hellenistic period, of which the most important one was the Musaeum in Alexandria, Egypt, which attracted scholars from across the Hellenistic world (mostly Greek, but also Egyptian, Jewish, Persian, among others). Although few in number, Hellenistic mathematicians actively communicated with each other; publication consisted of passing and copying someone's work among colleagues. Later mathematicians in the Roman era include Diophantus (c. 214–298 AD), who wrote on polygonal numbers and a work in pre-modern algebra (Arithmetica), Pappus of Alexandria (c. 290–350 AD), who compiled many important results in the Collection, Theon of Alexandria (c. 335–405 AD) and his daughter Hypatia (c. 370–415 AD), who edited Ptolemy's Almagest and other works, and Eutocius of Ascalon (c. 480–540 AD), who wrote commentaries on treatises by Archimedes and Apollonius. Although none of these mathematicians, save perhaps Diophantus, had notable original works, they are distinguished for their commentaries and expositions. These commentaries have preserved valuable extracts from works which have perished, or historical allusions which, in the absence of original documents, are precious because of their rarity. Most of the mathematical texts written in Greek survived through the copying of manuscripts over the centuries, though some fragments dating from antiquity have been found in Greece, Egypt, Asia Minor, Mesopotamia, and Sicily. Achievements Greek mathematics constitutes an important period in the history of mathematics: fundamental in respect of geometry and for the idea of formal proof. Greek mathematicians also contributed to number theory, mathematical astronomy, combinatorics, mathematical physics, and, at times, approached ideas close to the integral calculus. Eudoxus of Cnidus developed a theory of proportion that bears resemblance to the modern theory of real numbers using the Dedekind cut, developed by Richard Dedekind, who acknowledged Eudoxus as inspiration. Euclid collected many previous results and theorems in the Elements, a canon of geometry and elementary number theory for many centuries. Archimedes made use of a technique dependent on a form of proof by contradiction to reach answers to problems with an arbitrary degree of accuracy, while