Note 43 — Chapter I · PREAMBLE: ON THE ORIGIN OF WEAPONS.
Reading edition
See the hamus ferreus pointed at both ends in Demmin (p. 124); and the German Fussängel (p. 465). The larger caltrop was called tribulus, stylus or stilus (Veget. De Re Mil. iii. 24). The knights of mediæval Europe planted their spurs rowels upwards to serve the same purpose.