Commandos aren't a modern invention. Romans had those kind of units, called
praeventores,
exculcatores or
superventores.
The late roman army was over specialized : units of balistarii (artillery), heavy infantry (legio palatina), extra heavy cavalry (cataphractarii or clibanarii)... every tactical type of unit was "available".
My superventores was a frontier unit later promoted to the field army (a rare move, explained by both the bravery of this particular legio... and the lack of troops !), based in Mannatias, modern Nantes in France. Its aim was to protect the gaulish shores of pirates (Franks and Saxons).
those pirates were just looters, not invaders, so the traditionnal heavy infantry of the legio wasn't needed. Light equipped troops like superventores were perfect to intercept the pirates.

I've made this unit using a lot of sets from different manufacturers (Hät, Italeri, MiniArt, Redbox, even one Lucky toys !) very heavy "converted"

Some conversions :
Many more pics clicking here