2000-year-old vinegar, probably mixed with saltwater. And they pounded it just to say they did.
God that must have tasted horrible. Back in those days they sealed the amphoras with pitch and it likely gave the wine a strong sulfuric smell and taste. I wouldn’t be surprised however if it was still wine though seeing as the bacteria needed to convert the wine into vinegar would have a harder time surviving at those depths.
Feh, they're French.