#6: Silphium
Silphium was a famous Roman herb used for medicine, cooking, and even as birth control. People used its sap as a condiment and its roots for food. It was believed to cure everything from headaches to sore throats.
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Romans loved it so much that they overharvested it, and by the first century AD, silphium had vanished forever. There are even historical coins representing its likeness.