Sources : Boar (Wild)
Ovid [1st century CE] (The Metamorphoses, Book 8, 260-328): Its eyes glowed with bloodshot fire: its neck was stiff with bristles, and the hairs, on its hide, bristled stiffly like spear-shafts: just as a palisade stands, so the hairs stood like tall spears. Hot foam flecked the broad shoulders, from its hoarse grunting. Its tusks were the size of an Indian elephant’s: lightning came from its mouth: and the leaves were scorched, by its breath. - [Kline translation]
Pliny the Elder [1st century CE] (Natural History, Book 8, 78): Boars are very rough when mating; they fight with each other after rubbing against trees to harden their skin.
Isidore of Seville [7th century CE] (Etymologies, Book 12, 1:27): The boar (aper) is named after ferocity (feritate, with the F removed and a P added).
Gerald of Wales [c. 1146 – c. 1223] (Topographia Hibernica, chapter 19): In no part of the world are such vast herds of boars and wild pigs to be found ; but they are a small, ill-shaped, and cowardly breed, no less degenerate in boldness and ferocity than in their growth and shape. - [Forester translation, 1863]
Aberdeen Bestiary [circa 1200 CE] (folio 21v): The boar gets its name, aper, from its wildness, a feritate, the letter f being replaced by a p; for the same reason, it is called by the Greeks suagros, meaning wild.