If you thought putting anchovies on pizza was gross, brace yourself for this next post. The Roman Empire, being a wretched hive of scum and villainy for about the entirety of it’s hellion reign across most of Europe, wasn’t exactly shy about being off the wall crazy about some of its more questionable pleasures. From painting lavish dick pics everywhere to delighting in some healthy disembowelment in the gladiatorial arena, not much of these practices would be accepted in modern day society. Well, okay, except for maybe the first one.
One of the things the Romans were famously into, was soaking their food up in a sauce known as “Garum” or “Liquamen” which we’ve found archaeological evidence of in manufacturing, residue in pottery, and depicted in art and writing of the time. The sauce knew no societal bounds, common among people of all different classes and religions (evidence of a kosher option even exists) [1 & 3]. So, basically sounds like the Roman version of ketchup. How bad could it be?
Another liquid, too, of a very exquisite nature, is that known as “garuim:” it is prepared from the intestines of fish and various parts which would otherwise be thrown away, macerated in salt; so that it is, in fact, the result of their putrefaction. – Pliny the Elder, The Natural History 
Makes me want to hurl harder than a highlander tossing a log across long distances to impress his skirt wearing friends.
But was it really all that bad? Obviously, it was incredibly popular and how far removed would our taste buds really be from our Classical ancestors? Are we really any different, slathering our sushi rolls with eel sauce?
Evidently, garum was probably similar to popular fish sauces found in Vietnamese, Indochinese, and Turkish cuisine today. And based on our sources and the ancient recipe we’ve discovered concerning its production (A salt to fish ratio of 1:8), “the amount of salt used in the production process inhibited putrefaction and, hence, prevented any rancid smells. Bacterial fermentation, similar to that found in the production of cheeses, induced maturation of the product.”  Pliny claimed that the sauce itself smelled a bit funky, but what decent cheese doesn’t? And let’s not forget that even if it had a strong ode de parfum, he still called it exquisite. 
Probably seems strange that such a popular and maybe not all that gross sauce would just disappear then. But apparently, the sauce itself was fairly expensive, even some higher quality versions near the end of the Roman Empire’s life span would cost about $500 of today’s moolah. [3 & 4] It’s always baffling to me how unperturbed we are to have table salt readily available in a cupboard or at a restaurant, but it used to be a precious commodity that was heavily taxed and fought over. With a salt tax introduced among the empire, garum production became a bit too expensive since it was the necessary component that made it deliciously putridy. And with the collapse of power in the western half of the Roman Empire in the 5th century, the ownership of the Mediterranean seas became an indisputable playground for some good old fashioned piracy. 
If you’re not turned off by the process and are still curious how it tasted, however, you’re in luck! It’s starting to make a comeback.
Do you not realize that garum sociorum, that expensive bloody mass of decayed fish, consumes the stomach with its salted putrefaction?— Seneca, Epistle 95.