μὴ εἶναι βασιλικὴν ἀτραπὸν ἐπί γεωμετρίαν, Non est regia [inquit Euclides] ad Geometriam via
Reply given when the ruler Ptolemy I Soter asked Euclid if there was a shorter road to learning geometry than through Euclid's Elements.The "Royal Road" was the road built across Anatolia and Persia by Darius I which allowed rapid communication and troop movement, but use of ἀτραπός (rather than ὁδός) conveys the connotation of "short cut".
The Greek is from Proclus (412–485 AD) in Commentary on the First Book of Euclid's Elements, the Latin translation is by Francesco Barozzi, 1560) the English translation follows Glenn R. Morrow (1970), p. 57 http://books.google.com/books?id=JZEHj2fEmqAC&q=royal#v=snippet&q=royal&f=false.
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