Mostly, they died. Medical knowledge was really limited, even into the early 20th century. The “doctors” of the day had herbs and potions to ease pain, and they performed surgery, such as amputations, but much of anything beyond that was beyond their knowledge.
Well, they were pretty much SOL. Until the early 1900’s, doctors had an amazingly small toolkit for solving problems. There were some palliative measures you could take, but you had no antibiotics, no anaesthetics for surgery, and no notion of antisepsis or germ theory.
They could and did operate for stones, but it was an agonizing experience and many patients preferred to suffer.
There were some natural botanicals (e.g. curare) for fevers, and scary heavy metal compounds for things like venereal diseases, but if you got a major infection, you were pretty much as good as dead.
Actually, some civilizations that we don’t consider “modern” did perform surgery successfully. The BBC has a Medicine Through the Ages site that you might find interesting. It’s aimed at schoolchildren, but gives you an overview. The section on India contains the following:
Of course, while I was finding this site, several other people said the rest of what I was going to say.
Islamic medicine (see the foot of this Islamic Science page) is particularly worth noting: in 1000AD or so, it was centuries ahead of the West in many areas of medicine.