Caligae,the heavy sandals are the classic Roman army boot. These sandals were not worn outside by the Romans, rather they were regarded as indoor footwear, sometimes even carried by slaves to be changed into for such things as banquets .The caligae is comprised of three elements: the upper, the outer sole, and the inner sole. The upper is made of a single piece leather that is oiled to prevent decaying. The outer sole is made of one, two or three layers of leather, depending upon the requirement. The inner sole is usually one layer of leather sometimes two used to protect the foot from the ends of the hobnails.
PAS 2001 Mainz Caligae