During our Bouchercon panel, Lindsey Davis referred to a popular ancient fish sauce called garum, and I quickly pointed out it was invented by the Greeks, who called it garos. I've been asked about it so many times since that I thought I'd repost a slightly edited version of an article I wrote in November 2008.
The Greeks had a salty fish sauce called garos (γαροσ). It was incredibly popular in both Greece and (much later) Rome, where people would add it to almost anything. It was, in effect, the ketchup of the ancient world. (Nico's favorite food is eel in garos sauce.)
Since there was a fish called garos, or garon, in Greek, it's a fair bet the sauce was made mostly from that. I've been unable to discover what fish garos actually was. Not to worry, I can fudge it in my stories (but don't let Keith and Kathleen know that...I'll tell them I'm using the Greek word for authentic atmosphere).
The earliest references of which I'm aware are some lines in Aeschylus (fragments of the lost play Proteus) and Sophocles (fragments of the lost play Triptolemos), both of which refer to garos as stinking. Not a great advertisement, but the sauce was obviously popular enough that writers were referring to it and expecting everyone to understand. Since they were writing at the same time Nicolaos and Diotima are solving murders, I know I'm on solid ground using the sauce.
The stink is understandable. Although later Roman garum was made from carefully chosen gourmet fish, the original Greek version was made from leftover entrails.
Gary's theory, for what it's worth, is this: over-population was chronic in classical Greece, and children, especially small girls who were last in the feeding line, regularly went to bed hungry. Nothing that was even remotely edible was ever wasted. So when fishwives gutted the morning catch, they would have discarded the entrails into the large vats where some extra seawater would have been added, and the whole goopy mess allowed to ferment in the sun over weeks or months into garos. If this theory is correct then garos-the-fish is going to be whatever the main catch was.
When the Romans picked up the sauce from the Greeks, the ingredients and the name changed slightly. Garum isn't Latin. It's latinized Greek. Garum was made from whole fish, not only the offal. The Romans got very precious about the whole thing and would debate which species made the best sauce. Martial even talks about making it from, "mackerel still breathing its last." Later on, humble garum split into a range of gourmet sauces, each with their own names. Liquamen appears to be the original garum, and there was also allec, muria, and a pile of others. I haven't chased down any of these because by then, my characters are all shades in Hades.
Under Roman law it was illegal to make garum at home, the stench was that bad, so they had garum factories by the coast. The Greeks had no such rule, but practicality indicates garos would not have been made in Athens anyway, but Piraeus, the port town down the road, where the fisherman brought in their catch and the fishwives processed the fish. The garos would have been transported up to Athens in amphorae and sold in the Agora.