“Among the public works which he left at Rome were the splendid Baths named after himself, whose hot bath was built in such a way that, so the architects declare, it cannot be reproduced in the way he had it built. For it is said that the whole vaulting rested on gratings of bronze or copper, placed underneath it, but such is its size, that those who are versed in mechanics declare that it could never have been built in this way.”
(Historia Augusta, Life of Caracalla, 9, 4-5)