Wikipedia
Caligae
Caligae ( Latin; singular caliga) are heavy-soled hobnailed military boots known for being issued to Roman legionary soldiers and auxiliaries throughout the Roman Republic and Empire.
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.