so I was on the wikipedia page for pesto out of a random bout of curiosity and came across this gem: "The use of this paste in the Roman cuisine is mentioned in the Appendix Vergiliana, an ancient collection of poems where the author dwells on the details about the preparation of moretum." (moretum is a roman sauce that was a predecessor to pesto alla genovese)
so apparently this ancient roman poet just decided to write poems about how to make sauces