The word has been applied arbitrarily since classic times to various stringed instruments, some bowed and some twanged, probably owing to the back being much vaulted. Athanasius Kircher (Musurgia universalis, 486) applied the name of chelys to a kind of viol with eight strings. Numerous representations of the chelys lyre or testudo occur on Greek vases, in which the actual tortoiseshell is depicted; a good illustration is given in Le Antichità di Ercolano (vol. i. p1. 43). Propertius (iv. 6) calls the instrument the lyra testudinea. Joseph Justus Scaliger was probably the first writer to draw attention to the difference between the chelys and the kithara.