Pliny the Elder [1st century CE] (Natural History, Book 8, 14): There is the well-known case of the snake 120 feet long that was killed during the Punic Wars on the River Bagradas by General Regulus, using ordnance and catapults just as if storming a town; its skin and jaw-bones remained in a temple at Rome down to the Niunantine War. Credibility attaches to these stories on account of the serpents in Italy called boas, which reach such dimensions that during the principate of Claudius of blessed memory a whole child was found in the belly of one that was killed on the Vatican Hill. Their primary food is milk sucked from a cow; from this they derive their name. - [Rackham translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 2.33-34): [Chapter 2.33] Calabria swarms with water-snakes, and gives birth to the boa, which is a kind of snake said to grow to an immense size. First, the boa hunts herds of cattle, and he fastens himself to the udder of whichever cow is watered with the most milk. Fattened by continual sucking, he swells to such a state of satiety that no force is able to withstand his magnitude. Having plundered the animals, he brings the regions which he takes possession of to desolation. [Chapter 2.34] In the reign of Claudius, a whole child was seen in the belly of a boa slaughtered in the Vatican field. - [Arwen Apps translation, 2011]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 4:28): The boa (boas), a snake in Italy of immense size, attacks herds of cattle and buffaloes, and attaches itself to the udders of the ones flowing with plenty of milk, and kills them by suckling on them, and from this takes the name boa, from the destruction of cows (bos). - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Serpents 8.5): There is a serpent called boa in Calabria, as Solinus says, which grows to an immense size in this way: it first invades the herds of buffalo (or cows) which have plenty of milk, and attaches itself to their udders for a long time, being fattened and nourished to satiety so that no strength is able to resist its greatness, until at last it has depopulated the region of animals and brought it to ruin. This serpent was ravaging Dalmatia, as Jerome writes, when blessed Hylarion by a word of divine power forced the serpent to climb a pile of wood, and with a prayer he supposedly burned up the gigantic beast. Pliny, and the Hystoria of the Holy Fathers, describe this as a species of dragons so vast in size that they swallow deer and oxen whole. It is believed that the snake was of this species, which Regulus, the leader of the Romans - as the Roman Hystoria itself says - killed in Africa that was one hundred and twenty feet in length, and the skin stripped from the beast was brought to Rome for exhibition. Its jaws were also hung up in Rome for admiration. Pliny writes about this snake, that when it was captured, it was necessary to use catapults and various other weapons, as in the siege of a fort. - [Badke translation/paraphrase]