}}</ref> {{legenda|#ffcc00|Soy sauce}}{{legenda|#ff6600|Fish sauce}}]]
What's interesting, this kind of sauce was most popular in southern China, Indochina and Indonesia – but not further north, in most of China, Korea and Japan. Why? Well, in the north there was an easier-to-make alternative: the soy sauce. Fish sauce, on the other hand, was also produced in the Mediterranean Sea basin. Manufacture of various kinds of fish sauce (such as ''liquamen'', which was used for cooking, and ''garum'' , a table seasoning) was a big business in ancient Rome. I once visited in Barcelona the ancient ruins of a fish-sauce factory, which had stood next door to an ancient winery. Which means that must, which was used to make old-time mustard, was produced right next to fish sauce which wasn't much different from that which ketchup derives from.
Alas, the technology of fish-sauce production, unlike that of mustard, was gradually forgotten after the fall of the Roman civilization (it did survive somewhat longer in the Byzantine Empire). In Italy, ''garum'' was eventually replaced by another delicacy, made from salted, fermented and pressed fish roe, known as botargo. It wasn't until the Age of Exploration that Europeans could come across fish sauces again.
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By the 18th century, ketchup had become a familiar condiment throughout the British Empire. Jonathan Swift, known especially as the author of ''Gulliver's Travels'', gave "catsup" as an example of "home-bred British" food, as opposed to French "soups and fricassees", in one of his satirical poems. On the other hand, he He mentioned catsup in the same line as caviar and the aforementioned botargo, which shows that it was still classified as seafood.
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[[File:Mushroom ketchup Amazon.jpg|thumb|Modern mushroom ketchup]]
Ketchup could have been made from almost anything, so it was just a matter of time for until someone to get got the idea of making ketchup out of tomatoes. But who? The tomato plant isn't native to either Indonesia or the British Isles. Long after the first specimens were brought from America, Europeans were still apprehensive about it, because it reminded them of deadly nightshade, henbane bell and other related, highly toxic plants. It follows that tomato ketchup was invented on the same continent the tomato comes from. At the turn of the 19th century, tomato ketchup was already a popular condiment in the newly established United States of America. Just like other ketchups, it was enhanced by the addition of vinegar, spices and, starting in the 1840s, sugar (which also played the role of a preservative). Ketchup was starting to taste like it does today. And what did it look like? Old varieties of tomato were yellow (hence its Italian name, "''pomo d'oro''", or "golden apple", which has been borrowed into Polish and a few other languages). And ketchup was often strained and filtered, so it was a runny yellowish liquid rather than a thick red sauce.
It took a long time for the Polish people to learn what ketchup is and even longer for them to acquire a taste for it. First advertisements of "wallnut ketchup", an exotic sauce imported from Britain, started to appear in Warsaw newspapers around the middle of the 19th century.