Why were medieval armies so much smaller than Ancient ones?

by shotguntherifle

In 1415 Henry V invaded France with 6-9 thousand men. At the battle of Alesia 1500 years earlier Ceaser fielded 60 000 men and he was heavily outnumbered. So what changed

Midnight-Overlord

I believe u/FlavivsAetivs has a pretty relevant answer on this older post, Here