κρύπτη

Greek kryptein means "to hide." A kryptē was a hidden place—a concealed vault, a secret chamber. The word carried no particular association with death or religion. It simply named the act of putting something out of sight.

Early Christians in Rome buried their dead in underground galleries called catacombs. When churches were built above these burial sites in the 4th and 5th centuries, the underground chambers beneath the altar—where relics of saints and martyrs were kept—became known as crypts. The hidden place became holy. San Clemente in Rome has three layers: a 12th-century basilica above a 4th-century church above a 1st-century Roman house with a Mithraic temple. Each layer is the crypt of the one above it.

The architectural crypt spread across Europe. Canterbury Cathedral's crypt, built in 1070, is the largest in England. Chartres Cathedral's crypt dates to the 11th century and extends under the entire nave. Crypts stored relics, sheltered pilgrims, and occasionally held services. Some became pilgrimage destinations in their own right.

In the 20th century, "crypt" re-emerged in its original Greek sense. Cryptography—literally "hidden writing"—became the science of secure communication. Encryption, cryptanalysis, cryptocurrency: the Greek root for "hidden" now names the technologies that protect bank transactions, military communications, and private messages. The word went underground in both senses.