Cilantro falling out of favor from Ancient Rome is minor compared to Silphium which was an extremely popular Roman plant that went extinct, and nobody today knows what it was. Also Asafoetida, Liquamen, and Garum. Garum production was a large industry in Ancient Rome. Today, while there are some ostensibly traditional fish sauces made in parts of Italy, nobody knows for certain how Garum was made in Ancient Rome or if extant methods are related.