There is no royal road to geometry.

Reply to Ptolemy I Soter who 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) connotes a "short cut".

The Greek is from Proclus (412–485 AD) in his 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.