Allec is a fish sauce that the Romans made.
It was the paste, or sediment, that was left at the bottom of the container or barrel that other fish sauces such as garum, liquamen or muria were made in. It would probably have had some small, undissolved fish bones in it, and indeed amphorae (jugs) found at Massada that had contained Allec still had lots of small fish bones at the bottom.
Today’s versions would include Asian fish pastes and pissala, made in the south of France. Or perhaps you could even include Gentlemen’s Relish, depending on how far you were willing to cast the net on this one, as it were. In today’s versions, though, far more of a fish taste may come through than would have in the Roman version, as the Roman version had been fermented and aged for several months. It may have been just more of a salty spread, with the fishy taste behind that a bit of a bonus.
Some food historians feel that it wasn’t added during cooking, but was used as a condiment on plates, or simply spread on bread.