I once had 10 civil war-tech troops with rifles lined up against a fort with ONE bow and arrow troop. I lost every single one of my troops and that's the last time I've played Civ 3 in my life. Hopefully they addressed this issue...
(PS: once a friend lost a battleship to a stone age militia in the original Civ)
Civ III battles are best thought of as dice rolls like the board game Risk. If you have more modern units you get to roll more dice but there's still a small chance archers defeat musketmen.
Civ V definitely solved the issue by separating unit strength and their HP. Not sure about Civ 4, but I think it applies there too.
I lost a nuke to a phalanx in Civ 1. Still salty about that _decades_ later.
It was a dud
tbh that's a civ rite of passage