The history of the insole:
The history of the insole goes back to the Roman era. Once the Romans had gained a foothold, they built stone roads and military camps, which later became real cities. In order for the Roman Empire to become one of the largest empires in world history, the army often had to walk long distances on the built stone roads.
The long marches with heavy equipment on their backs left marks on the feet of many soldiers. To counteract the various foot diseases, the Romans developed the first leather soles for their hiking boots. These boots used by the Roman military were called 'caligae'. They are still known today under the term "Roman sandals".
The caligae were made from one piece and weighed around 1,300 grams. The integrated sole was around 8 millimeters thick. The underside of the sole did not have a special profile, but was studded with 80-90 iron nails with hemispherical heads. These nails held the sole together. In addition, the metal nails in the soles were used for a better grip while walking.
In addition, the nails protected the sole from wear and tear. Certainly the metal nails under the soles were not particularly pleasant for the Romans and did not promise particularly high comfort for the feet. Still, the benefits outweighed the benefits.