1911 Encyclopædia Britannica/Crypto-porticus
CRYPTO-PORTICUS (Gr. κρυπτός, concealed, and Lat. porticus), an architectural term for a concealed or covered passage, generally underground, though lighted and ventilated from the open air. One of the best-known examples is the crypto-porticus under the palaces of the Caesars in Rome. In Hadrian’s villa in Rome they formed the principal private intercommunication between the several buildings.