Even though the term has a medieval origin, this kind of device was first described by Julius Caesar, in the seventh book of his "Commentarii de Bello Gallico" (Commentaries on the Gallic Wars), who employed the device during the siege of Alesia. Caesar writes they were called "lilies" for their resemblance to the flower of the same name. Later Roman examples can be seen at Rough Castle on the Antonine Wall in Great Britain.