E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Aurelius Antoninus was so called because he adopted the Gaulish caracalla in preference to the Roman toga. It was a large, close-fitting, hooded mantle, reaching to the heels, and slit up before and behind to the waist. Aurelius was himself born in Gaul, called Caracal in Ossian. (See CURTMANTLE.)