[Antoninus]

I've always wondered if there wasn't a humane method of euthanizing soldiers critically wounded in battle during Roman times. It seems needlessly cruel to keep a valiant warrior alive and in extreme pain in a day when no medicine or anodynes were available and death was inevitable, whether it came quickly and mercifully or with grim delay.

Field doctors were often better than you think in Roman times. Procopius, writing in the 6th century AD, describes a couple of soldiers, both Roman and Gothic, who had horrible injuries and yet survived. The Goth had received a dozen or so stab wounds and had lain under a pile of corpses outside Rome, but lived.

A terrible wound wasn't always a death sentence.

[VOA]

Field doctors were often better than you think in Roman times.

On a recent History Channel show, it was mentioned that infantry soldiers
didn't attain the survival rates of the Roman legions until fairly
recent times.
(probably when the French started to really work on battlefield
surgery in Napoleonic times, I'd inexpertly guess)