E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The divine weed, vervain, said by the old Romans to cure the bites of all rabid animals, to arrest
the progress of venom, to cure the plague, to avert sorcery and witchcraft, to reconcile enemies, etc. So highly esteemed was it that feasts called Verbenlia were annually held in its honour. Heralds wore a wreath of vervain when they declared war; and the Druids held vervain in similar veneration.