Euclid was once employed as a tutor of mathematics in the royal household of King Ptolemy I, who complained about the difficulty of the theorems which Euclid expected him to learn.

When the king asked whether there might be an easier way to approach the subject, Euclid gently reproached him: "Sire," he said, "there is no royal road to geometry."

[Euclid's The Elements remained the standard geometry textbook until the end of the nineteenth century.]