http://www.pompeii-food-and-drink.org/garum.htm
Garum was a popular fish sauce condiment. It was made by the crushing and fermentation in brine of the intestines of fish such as tuna, eel, anchovies, and mackerel. Because the production of garum created such an unpleasant smell, its fermentation was relegated to the outskirts of cities. The finished product was quite mild and subtle, and was mixed with wine, vinegar, pepper, oil, or water to enhance the flavor of many dishes. Garum is similar to fish sauce used today in Thai and Vietnamese cooking.
The preparation of Worcestershire sauce is reportedly a foul thing as well... But I couldn’t imagine life without it. :-)