Helmet ridges were popular in certain regions and eras of the Empire to deflect downward-striking blows - the popularity of the ridge waxed and waned as it was needed. When the Romans encountered the Dacians with their long, curved-blade falx, ridged helmets became very popular, as a downward strike with the falx could glance off of one’s helmet… and smoothly slide down to gouge out a poor legionary’s eye, or poke into his soft, squishy brain. The ridge there causes a blow to lose momentum, or deflect outward, rather than letting it slide inwards towards the unprotected face.
Helmet ridges were popular in certain regions and eras of the Empire to deflect downward-striking blows - the popularity of the ridge waxed and waned as it was needed. When the Romans encountered the Dacians with their long, curved-blade falx, ridged helmets became very popular, as a downward strike with the falx could glance off of one’s helmet… and smoothly slide down to gouge out a poor legionary’s eye, or poke into his soft, squishy brain. The ridge there causes a blow to lose momentum, or deflect outward, rather than letting it slide inwards towards the unprotected face.