Garum was the ancient Roman fish sauce made by fermenting fish with salt.
Small fish, fish scraps, and salt were layered and left to ferment, often in the sun. The liquid that drained from the mixture was prized as a powerful seasoning. Production varied by region and quality, and the sauce could be flavored with herbs or wine. Garum was used in many Roman dishes in much the way modern cuisines use salty fermented sauces.
Garum was traded widely around the Mediterranean, with production centers in places including Hispania and North Africa. It is related to liquamen, a term that later became common in Latin culinary writing, and the two words can overlap in historical sources. Garum was not a sweet grape reduction; that product was called defrutum.