Sources : Elk

Julius Caesar (Commentaries on the Gallic and Civil Wars, Book 6.27): There are also [animals] which are called elks [alces]. The shape of these, and the varied color of their skins, is much like roes, but in size they surpass them a little and are destitute of horns, and have legs without joints and ligatures; nor do they lie down for the purpose of rest, nor, if they have been thrown down by any accident, can they raise or lift themselves up. Trees serve as beds to them; they lean themselves against them, and thus reclining only slightly, they take their rest; when the huntsmen have discovered from the footsteps of these animals whither they are accustomed to betake themselves, they either undermine all the trees at the roots, or cut into them so far that the upper part of the trees may appear to be left standing. When they have leant upon them, according to their habit, they knock down by their weight the unsupported trees, and fall down themselves along with them. [The account following this one (6.28) compares the size of another beast to the elephant; this may be the source of the confusion of the elk and elephant.]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Quadrupeds 4.5, 4.7): [Thomas describes the elk under the name aloy and alches.] [Quadrupeds 4.5] Aloy is an animal almost like a mule, whose knees cannot be bent, like elephants. Therefore it does not lie down while he sleeps, but leans against a tree. The tree is cut down by the hunters and it falls. Thus it is taken; otherwise it is difficult to tame it, for it will run with an incomprehensible speed. [Quadrupeds 4.7] Alches, as Solinus says, is an animal similar to a mule in all respects, except that it has a lip so extended in the upper part, that unless it retreats to its hind legs, that is, it goes backwards, it cannot graze on the grass. This signifies some dialecticians of the present time, who, being too eager to listen to the arts, neglect grammar. So let such people know, because if they want to feed on true knowledge, let them go back to the first grammatical foundation. Or it also signifies those who, while eager for contemplation, forget their sins and weep not. - [Badke translation/paraphrase]