The Caligula (named after the emperor Caligula) was the standard issue army boot of the day.  The Roman legion’s simple, sturdy sandal design was worn for centuries from Britain to Byzantia (Istanbul)  Egypt to Spain.  The soles of these sandals were hobnailed for durability, traction and an offensive weapon.  These iron hobnails also produced a very intimidating sound for the marching soldiers demoralizing their enemies with terror.  The hobnail has been used by armies throughout history for these reasons, most recently and infamously by the Nazis in WWII.