The first known description of the bonnacon comes from Pliny the Elder’s Naturalis Historia:
There are reports of a wild animal in Paeonia called the bonasus, which has the mane of a horse, but in all other respects resembles a bull; its horns are curved back in such a manner as to be of no use for fighting, and it is said that because of this it saves itself by running away, meanwhile emitting a trail of dung that sometimes covers a distance of as much as three furlongs (604 meters or 1,980 feet), contact with which scorches pursuers like a sort of fire."
context: https://en.wikipedia.org/wiki/Bonnacon