A Roman caliga was typically equipped with up to 90 iron nails per sole, although other sources mention around 50 nails, often arranged in specific patterns. The hemispherical heads of the nails functioned like modern spikes, giving the smooth leather sole a profile that provided the necessary sure footing and traction on difficult terrain such as clay or stone. Furthermore, the nails protected the sole from premature wear and, thanks to their ergonomic arrangement, enhanced comfort while marching.