Caligae are heavy-soled hobnailed military sandal-boots that were worn as standard issue by Roman legionary foot-soldiers and auxiliaries, including cavalry.
A reproduction of a Roman caliga
From below, showing hobnails
An original caliga found at Qasr Ibrim, Egypt, c. 1st century BC – 1st century AD
In footwear, a hobnail is a short nail with a thick head used to increase the durability of boot soles or provide traction.
Caligae
…Caligae (Latin; sg.: caliga) are heavy-soled hobnailed military sandal-boots that were worn as standard issue by Roman legionary foot-soldiers and auxiliaries, including cavalry. Caligae (sg.: caliga) are…
A pair of hobnailed boots
Roman hobnails were shoe tacks, a type of clinching nail; the narrowing tip was turned by a last held inside the sole as the nail was driven. So the tip did a U-turn back into the sole, clinching the nail in place.