The caligae can resemble modern sandals but were actually marching boots. Sandals proper 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 open design of caligae allowed for the free passage of air to the feet and, unlike modern military boots, was specifically designed so as to reduce the likelihood of blisters forming during forced marches, as well as other disabling foot conditions like tinea or trench foot. Socks were not normally worn with caligae, although in colder climates such as Britain, woolen socks were used.
Caligae were constructed from three leather layers: an outsole, the middle openwork layer which formed the boot's upper, and an insole. They were laced up the center of the foot and onto the top of the ankle. Additionally ironhobnails were hammered into the soles to provide the caligae with reinforcement and traction, and were also an effective weapon against a fallen enemy.
Various other types of leather footwear were worn within the Roman empire. The carbatina was a sandal made from one piece of leather with a soft sole and openwork upper fastened by a lace. A soccus was a sole without hobnails and a separate leather upper. A calceus was a hobnailed footwear secured by laces. A solea was a simple sandal with a thong between the toes and a hobnailed sole. Women wore sandals similar to those of men, but they were of softer, finer leather. Winter shoes were usually cork-soled. Sometimes the soles were thickened to provide the imitation of height.
Caligula, the emperor whose nickname stemmed from the diminutive of caliga (meaning "little boot"). His father Germanicus was a well esteemed military officer. Germanicus' soldiers nicknamed Caligula, who stayed in camp with them often, after the amusing legionary costume he wore as a child. When Caligula wore caligae as emperor, he covered them with precious jewels.