In ancient Rome, wine was drunk diluted with water, as discussed in this question.
When did it become common practice not to dilute wine, but to drink it as is?
I tried to look, and found nothing much on diluting after the Roman Empire. I know monasteries made wine, but I don't know if they drank it diluted or not. There's a scene in The Three Musketeers where Porthos is a guest at a house, and is disgusted to be served diluted wine. So by that point, (or by the time Dumas was writing,) diluting wine with water was associated with poverty/stinginess, and wine was commonly drunk undiluted. But I have nothing in between those two points in time.
(Note this question is specifically about wine, rather than other alcoholic drinks, such as absinthe.)