Fish was the fundamental ingredient of "garum", the favorite sauce of the Romans
The recipe which follows is taken verbatim from De re coquinaria by Apicius, considered the first great chef in history.
The sauces, in general, they were much loved by the Romans, who used them to accompany practically any type of dish.
The white sauce suggested by Apicius, it was ideal for giving flavor to boiled meat.
The very simple recipe consisted of mixing these ingredients to perfection:" pepper, garum, wine, rue, onion, pine nuts, aromatic wine, a little macerated bread to thicken and oil".
The garum, which I have covered in this post https://www.pilloledistoria.it/1787/storia-antica/garum-liquamen-salsa-preferita-dai-romani, was a sauce based on fish entrails left to soak in the sun for which the Romans were literally crazy, as well as olive oil it was also a fundamental food in the diet of the time.