Sources : Boar
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): Wild pigs breed once a year. The boars are very rough when mating; at this period they fight each other, hardening their flanks by rubbing against trees and plastering their behinds with mud. The females are fiercer when with young, and this is more or less the same in every kind of wild animal. Male boats do not mate till one year old. In India they have curved tusks 18 inches long: two project from the jaw, and two from the forehead like a calf's horns. The wild boar's hair is a sort of copper color; that of the other species is black. But the hog genus does not occur in Arabia. - [Rackham translation]
Isidore of Seville [7th century CE] (Etymologies, Book 12, 1.27): The ‘wild boar’ [aper] is so named from its ferocity [feritas],with the letter f removed and a p substituted. Whence he is also named “wild” in Greek, for everything that is wild and untamed, we call, with loose usage, ‘of the country’ [agrestis]. - [Barney, Lewis, et. al. translation]
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.
Thomas of Cantimpré [circa 1200-1272 CE]: (Liber de natura rerum, Quadrupeds 4.3): The wild boar, as the Liber rerum says, is powerful, and accepts no instruction of good behavior at any time, but it is always savage and defiant. It is of a dark color. It has large and curved tusks of a half-foot long, which are fit for incising. But this thing about the teeth is quite extraordinary, which is that in a live beast they are able to be used as a weapon, but having been removed from the boar they are proven to truly lose their power of cutting. Some cruel men of the age may be branded as wild boars, who receive literally no teaching of good works, but are always judged selfish and ferocious, black, that is, base and impious in their actions. They have crooked teeth in themselves, because he who injures another injures himself first in his conscience through the purpose of evil. He has half-foot teeth, because although they hurt the body, they have no control over the soul. And this is worthy of such: as long as they live, they can sow only; But when they are dead and cast into hell, their tyranny ceases. This animal, if it is attacked by hunters in the morning before it performs its urinary digestion, is easily tired. If, however, he urinates before or in the meantime when he is being hunted, he is difficult to capture, but he does not give in when tired, for he stops and disguises his fatigue with a stiff fury, offering a duel to the hunter. However, he does not presume to strike or attack a man, unless he has first received a blow from him. And so a man should be careful, because unless he gives a fatal wound at the first blow of the spear's point between the arm and the side ribs, he may be in danger of his life, unless he may find a tree nearby which he can climb for refuge, or press himself with all his limbs in a lower place on the rest of the ground. He will, however, endure as long as he lies thus assisted by his neighbor. For, as we have said, his teeth are bent and curved, as if they are capable of inflicting death with the most terrible weapons, but they cannot touch anyone unless the teeth are raised and upright. He runs into the bushes to get rid of the dogs that follow him or even hold him in their teeth. The boar surpasses all beasts in listening. The males, as Pliny says, are most rough during intercourse, and they are more severe to the female during birth; but in general they are similar to every birth of beasts. As the Experimentator says, fresh and warm boar's dung is an excellent remedy against bleeding from the nose. The boar has in his mouth on the right the form of a shield, and he opposes it to the spear and the lance. Pierced with a spear or a sword, he actually walks forward against the shaft. As the aforesaid author says, the flesh of swine is cold and moist, and this especially in domestic pigs; it lactates more than the rest: it is more moist and turns into various fluids and putrefactions, especially if it finds an ill-disposed stomach. If a sow eats many acorns when she is pregnant, she will miscarry. It is characteristic of swine to seek food buried in the ground, and to fill their mouths on muddy and cheap things. The first-born pig will be smaller and weaker than the others. When she has many children, then the sow will have little milk. In warm regions the piglet of the pig is better in the summer, but in cold regions the opposite is true; and this because of the bad weather of those regions. In India the tusks of the wild boars are a cubit long. There are also boars, from whose foreheads horns extend like those of calves. In Arabia, however, the pig species does not live. - 
Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.6): The boar is so fierce a beast, and also so cruel, that for his fierceness and his cruelness, he despiseth and setteth nought by death, and he reseth full piteously against the point of a spear of the hunter. And though it be so that he be smitten or sticked with a spear through the body, yet for the greater ire and cruelness in heart that he hath, he reseth on his enemy, and taketh comfort and heart and strength for to wreak himself on his adversary with his tusks, and putteth himself in peril of death with a wonder fierceness against the weapon of his enemy, and hath in his mouth two crooked tusks right strong and sharp, and breaketh and rendeth cruelly with them those which he withstandeth. And useth the tusks instead of a sword. And hath a hard shield, broad and thick in the right side, and putteth that always against his weapon that pursueth him, and useth that brawn instead of a shield to defend himself. And when he spieth peril that should befall, he whetteth his tusks and frotteth them, and assayeth in that while fretting against trees, if the points of his tusks be all blunt. And if he feel that they be blunt, he seeketh a herb which is called Origanum, and gnaweth it and cheweth it, and cleanseth and comforteth the roots of his teeth therewith by vertue thereof. - [Steele]