Pliny the Elder [1st century CE] (Natural History, Book 8, 32): In its neighborhood there is an animal called the catoblepas, in other respects of moderate size and inactive with the rest of its limbs, only with a very heavy head which it carries with difficulty, so it is always hanging down to the ground; otherwise it is deadly to the human race, as all who see its eyes expire immediately. - [Rackham translation]

Aelianus [2nd century CE] (On the Characteristics of Animals, Book 7, chapter 6) : Libya ... produces the animal called the Katobleps. In appearance it is about the size of a bull, but it has a more grim expression, for its eyebrows are high and shaggy, and they eyes beneath are not large like those of oxen but narrower and bloodshot. And they do not look straight ahead but down on to the ground: that is why it is called ‘down-looking’. And a mane that begins on the crown of its head and resembles horsehair, falls over its forehead covering its face, which makes it more terrifying when one meets it. And it feeds upon poisonous roots. When it glares like a bull it immediately shudders and raises its mane, and when this has risen erect and the lips about its mouth are bared, it emits from its throat pungent and foul-smelling breath, so that the whole air overhead is infected, and any animals that approach and inhale it are grievously afflicted, lose their voice, and are seized with fatal convulsions. This beast is conscious of its power; and other animals know it too and flee from it as far away as they can. - [ Scholfield translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 30.22): The catoblepas is produced close to the river Nigris. It is a sluggish beast of medium size, and bears its burdensome head with difficulty. It has a destructive glance, for whoever encounters its eyes dies immediately. - [Arwen Apps translation, 2011]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Quadrupeds 4.28): Cathapleba is an animal near the spring called Niger, as Pliny and Solinus write, a small and slow beast living near the banks of the Nile. It has a heavy head with a look so pestilential, that those who look into his eyes immediately fall and lose their lives. - [Badke translation/paraphrase]

Bartholomaeus Anglicus [13th century CE] (Liber de proprietatibus rerum, Book18.15; 18.16): [Book18.15] ...there beside is a wilde beast that is called Catobletas, and hath a lyttle body, and nice in al members, and a great head hanging alway, toward the earth, and els it were great noyeng to mankinde: for all that sée his eyen, should dye anone... [Book 18.16] ...Among the Hisperies and Aethyopes is a well, that many men suppose is the head of Nylus [Nile River], and there beside is a wilde beast that is called Catobletas, and hath a lyttle body, and nice in al members, and a great head hanging alway, toward the earth, and els it were great noyeng to mankinde: for all that sée his eyen, should dye anone, and the same kinde hath the Cockatrice... - [Batman]