Travelers in northern Spain once carried live roosters into the woods for protection against a snake no bigger than a ruler. This episode traces the basilisk from its Greek name meaning little king, through Pliny the Elder's Natural History description of a crowned serpent from Cyrene that moves upright, withers grass, breaks stones with its breath, and can only be killed by the odor of a weasel.

We line up Pliny's account against the earlier, more naturalistic poem Theriaka by Nicander of Colophon and argue the original was a spitting cobra, with the weasel standing in for the mongoose. Then we follow the myth's medieval mutation into a rooster-hatched chimera tied to miasma theory and the dog star Sirius, its role in alchemical recipes for Spanish gold, the urban legends of Warsaw and Vilnius, and its final life as a metaphor for paralyzi ...