While largely true that Euro-Grapes are grown on American blight-resistant wild grape root-stock, many of the grape varieties of antiquity have survived, in Italy, Greece, and even in out-of-the-way Roman outposts like Rumania.
I have read that ancient wine was thick and potent, and that it was usually drunk mixed with water, and even flavored with drugs and herbs. Can't wait to see what these archeologists come up with.
Couldn’t have been terribly more potent than present wines. Maximum alcohol content without distillation is around 16%.
Higher concentrations the alcohol, which is essentially yeast urine, kills the yeast.