Murri was a fermented sauce that was used a great deal in Arabic cooking, mostly used from the 1200s to the 1400s.
It wasn’t meant to be consumed on its own, or used at the table; its strong, salty taste made it ideal for use as a cooking ingredient in small amounts. It was used as omnipresently as soy sauce now is in Asian cooking, and likely had a fermented taste similar to some of the (cheaper) soy sauces that incorporate grain.
It was made from barley meal, sometimes with wheat flour mixed in. It was occasionally flavoured with some cinnamon or saffron. The flour was moistened, kneaded into loaves, covered with fig leaves or put in covered containers, and let ferment and rot for 4 months. A furry mould would grow on top of it. To use, you would mix it up the quantity needed in water.
It was also made in Arab-occupied Spain.
A version made in Byzantium was more elaborate. One Byzantine recipe called for carmelized honey, ground toasted bread, a starch, toasted and ground anise, fennel and nigella seeds, saffron, celery seed, carob, walnuts, sugar syrup, quinces, salt, and water. The mixture was simmered down a 1/3, then strained, lemon juice was added, and then it was put into a covered container to ferment.