Sources : Swordfish

Pliny the Elder [1st century CE] (Natural History, Book 9, 21): There is a small animal shaped like scorpion, of the size of a spider. This attaches itself with a spike under the fin of both the tunny and the fish called swordfish, which often exceeds the size of a dolphin, and torments them so painfully that they frequently jump out of the water into ships. This is also done on other occasions from fear of the violence of other fish, especially by mullet, which are so exceptionally swift that they sometimes leap right over ships that lie across their path. - [Rackham translation]

Isidore of Seville [7th century CE] (Etymologies, Book 12, 6:15): The swordfish [gladius] is so called because it has a snout like a sword [gladius, “sword”]; because of this it pierces ships and sinks them. - [Barney, Lewis, et. al. translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Marine monsters 6.26): A swordfish is a sea monster, as Pliny and Isidore say, having its name from the fact that it has a beak as sharp as a sword, with which it pierces ships and sinks them. - [Badke translation/paraphrase]

Albertus Magnus [ca. 1200-1280 CE] (De animalibus, Book 24, 60): Swordfish is the fish which our countrymen call the "soldier" [militem]. This fish has the same sort of skin as a dolphin, but has the shape of a sturgeon without the latter’s coarse, rough exterior. Where its body terminates in a tail, instead of tapering down to a slender extremity, it ends abruptly with a broad, bifurcated tail that gives the body a lopped-off appearance. It is dubbed the swordfish [gladius] because its snout is more than a cubit and a half in length and narrows straightaway to the point and shape of a sword; the sword is made of a dark-colored substance, harder than horn but softer than bone. Beneath the snout it has a mouth constructed not for sucking like a sturgeon but for eating like a salmon. Its lower jaw or chin is triangular in shape and well supplied with teeth. With its sword it slays fish and reportedly impales the sides of boats. I have seen dead intact specimens of this fish and examined them at first hand. The swordfish is a very fatty fish with a layer of adipose flesh on its back like a pig. - [Scanlan]