Warning. This one is a bit fishy...
Fish heads and guts were made into a mash and then the liquid left to ferment for weeks out in the sun. The end product was strained and bottled, and sold as a condiment for cooking.
So odoriferous were the Roman garum factories that they were located as far as possible from populated areas and to this day archaeologists can still smell fishy stuff in the soil.
Some of the more diverse uses of garum was to cure one of freckles.
And many containers of kosher garum were found in the preserved ruins of Pompeii suggestive of another holocaust incident on the chosen people.
(By the way. Where is the cooking section?)