Histories
Herodotus
Herodotus. Godley, Alfred Denis, translator. Cambridge, MA; London: Harvard University Press; William Heinemann, Ltd., 1920-1925 (printing).
Horses have the endurance to bear the Scythian winter; mules and asses cannot bear it at all; and yet in other lands, while asses and mules can endure frost, horses that stand in it are frostbitten.