Overview
Caligae are not sandals but sturdy military boots: a one-piece leather upper cut into openwork straps is laced over the foot and nailed to layered soles set with iron hobnails. The open design let air circulate and water drain on long marches.
How it is worn
They are laced up the centre of the foot and around the ankle, worn with or without woollen socks depending on the climate. The hobnails gave grip and long wear and, massed, let a marching column be heard and felt; soldiers even used them to trample a fallen enemy.
History
Caligae were standard issue for legionaries and auxiliaries into the early Empire — the emperor Gaius earned the nickname Caligula, little boot, as a child in camp. From the second century they gave way to more enclosed boots as the army changed.