Would soldiers of the ancient and medieval world be terrified by the appearance of soldiers of today?
let’s use a modern special operations soldier for an example:
Here is a group of US army Delta operators:
Most countries have guys with similar missions and similar kit. These guys are basically extremely well trained light infantry. They are trained to survive and function independent of command for long periods of time, they adapt, they innovate in the field. A pair of these guys is a total force multiplier.
They wear lightweight, close fitting ballistic armor, and kevlar helmets, but only what they deem needed for the mission at hand. they have the luxury of picking their individual weapons to suit the needs of the mission and thier own specialties within the unit.
A medieval or ancient solder would NOT be terrified of these guys. (Not at first!) they’ve seen men in helmets, in cuirass or gambason before.
the cut and fit for the armor would be alien to them, but they WOULD recognize the wearable kit as armor of a sort (they would wonder How effective this strange cururiass and helmet might be)
they’d be confused what the other equipment is - but not afraid of it. Not till they learned the hard way that the odd black item on a strap that resembles a… musical instrument? Or some such can do to a man from clear across the field, with not much more noise than a man with a crossbow. Or that the bizarre eyewear attached to the helmet can turn the darkest night into day - without a torch to light the way.
that’s what would terrify them.
not the appearance of the men.
but the capabilities of the equipment, and how those men use it. the fact that just 4 of these guys could creep like specters into a camp or castle, eliminate the sentries silently - and Elimate thier command elements with little difficulty - that would be terrifying.
or sneak in blow up something with a charge bigger than a smallish brick - when and where they see fit - that would be terrifying.
or killing a field commander from “nowhere”from an “impossible distance” - that would be terrifying.
or mowing down an entire battle line of soldiers with a light machine gun - that would be terrifying.