Note 8 — Chapter I · ROGER BACON: THE TRUE AND THE LEGENDARY.
Reading edition
The pentageron, or pentagramma, is a mystic figure produced by prolonging the sides of a regular pentagon till they intersect one another. It can be drawn without a break in the drawing, and, viewed from five sides, exhibits the form of the letter A (pent-alpha), or the figure of the fifth proposition in Euclid’s First Book.