Sources : Hippopotamus

Aristotle [ca. 350 BCE] (De animalibus, Book 2, 4.1): The Egyptian river-horse has a mane like a horse, and a cloven hoof like the ox; it has a flat face; the talus is like that of other animals with cloven hoofs, and it has large projecting teeth; it has a tail like a hog, and utters a sound like the neighing of a horse; it is about the size of an ass, and its skin is so thick that shields are made of it; its intestines are like those of a horse or ass. - [Cresswell translation, 1887]

Pliny the Elder [1st century CE] (Natural History, Book 8, 39-40; 11, 93): [Book 8, 39] A monster of still greater height is also reproduced in the Nile, the hippopotamus, which has cloven hoofs like those of oxen, a horse's back, mane and neigh, a snub snout, a boar's tail and curved tusks, though these are less formidable, and with a hide that supplies an impenetrable material for shields and helmets, except if they are soaked in moisture. It feeds on the crops, marking out a definite portion beforehand for each day, so it is said, and making its footprints lead out of the field, so that no traps may be laid for it when it returns. [Book 8, 40] A hippopotamus was exhibited at Rome for the first time, together with five crocodiles, by Marcus Scaurus at the games which he gave when aedile [58 BCE]; a temporary channel was made to hold them. The hippopotamus stands out as an actual master in one department of medicine; for when its unceasing voracity has caused it to overeat itself it comes ashore to reconnoiter places where rushes have recently been cut, and where it sees an extremely sharp stalk it squeezes its body down on to it and makes a wound in a certain vein in its leg, and by thus letting blood unburdens its body, which would otherwise be liable to disease, and plasters up the wound again with mud. [Book 11, 93] The skin of the hippopotamus is so thick that it is used for the points of spears, and yet its mind possesses a certain medical ability. - [Rackham translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 32.30-31): [Chapter 32.20] The hippopotamus is nurtured by this same land and river. It has a horse-like back, mane and neigh, a turned-up nose, cloven hooves, tusks like a wild boar’s and a twisty tail. In the night, it lays waste the grain-fields. With crafty cunning, it proceeds towards these backwards, so that when it goes to return, its deceptive footprints ensure no ambush is prepared for it. [Chapter 32.31] When overfull with excessive feasting, it seeks newly cut reeds, and walks to and fro through them for so long a time, that the sharp ends of the plants wound its feet, and its satiety is lightened by the flow of blood. Then it plasters the area with mud, until the wounds heal into scars. Marcus Scaurus was the first to bring hippopotami and crocodiles to Rome. - [Arwen Apps translation, 2011]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:21):The hippopotamus is so named because it is similar to the horse in its back, its mane, and its neighing; its snout is tilted back, and it has boar-like teeth and a curled tail. It stays in the water during the day and grazes on crops at night. The Nile also produces this animal. - [Barney, Lewis, et. al. translation]

Alexander Neckam [1147-1217 CE] (De naturis rerum, Book 2.38): The hippopotamus, which lives in the Nile, has a horse's back and mane and neigh, an upturned snout, bifurcated hooves, boar's teeth, and a twisted tail. At night it grazes on crops, to which it goes backwards with cunning, so that its deceptive footprints ensure that no traps are prepared for it when it returns. It will be easy to adapt this to the elaborate frauds of the unfaithful, who do what Solinus says about the beast. In the same way, when the hippopotamus is too full from excessive eating, it looks for fresh-cut reeds, through which it walks for long a time until its feet are wounded by the sharp stalks, so that it is lightened by the flow of blood. Then it covers the wounds with mud, until the wounds become scars. - [Wright/Badke]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Marine monsters 6.20, 6.27): [Thomas describes the hippopotamus under the names equus fluminis (river horse) and ypotamus.] [Marine monsters 6.20] The river horse {equus fluminis), as Aristotle says, is a monster of wonderful form in the eastern parts. It can live on land and in water equally. It has hair like a horse; its feet are cloven, and it has hooves like an ox, and it has a lofty face, and it has a tail like a pig, and it neighs like a horse. Its skin is very thick, and its insides are like those of a horse. Its size is like that of an ass. [Marine monsters 6.27] Ypotamus, as Pliny says, is a beast that lives in the river Nile. It is born on land. It is equally powerful in the water and on the land. It is generally larger than elephants. It has a beaked face, forked claws, a crooked tail, and hooked teeth, like the teeth of boars; but its back is just like a horse. At night it grazes on the crops, to which it goes as if walking backwards, so that no ambush can be prepared for it when it returns by the false trail. When this beast is distended with excessive abundance of food it seeks for newly cut reeds, or the points of thorns, and rolls between them for a long time, until by their incisions a certain vein in the leg is wounded, so that it is soaked with a minute amount of blood. It receives wounds in the feet more readily than in other parts of the body. It takes care of the wound carefully, until the wound is reduced to a scar. They are mainly found in the region of India. Its back is impenetrable unless wet with water. A shield is made from its skin. Scaurus brought this beast with five crocodiles to the games of the Romans, as Pliny says. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book13.29): For some Fish séeke theyr meate onelye in Water, and some by night upon the land, as Hippotamus the water horse, and hath that name, for he is lyke to a horse in ridge & in mane, as Isidore saith, and abideth in water on the day, and eateth corne by night, and is bread in the river Nilus, as Isidore sayth. - [Batman]