Originally, crypts were typically found below the main apse of a church, such as at the Abbey of Saint-Germain en Auxerre, but were later located beneath chancel, naves and transepts as well. Occasionally churches were raised high to accommodate a crypt at the ground level, such as St Michael's Church in Hildesheim, Germany.
"Crypt" developed as an alternative form of the Latin "vault" as it was carried over into Late Latin, and came to refer to the ritual rooms found underneath church buildings. It also served as a vault for storing important and/or sacred items.
"Crypta", however, is also the female form of crypto "hidden". The earliest known origin of both is in the Ancient Greek κρύπτω (krupto/krypto), the first person singular indicative of the verb "to conceal, to hide".
First known in the early Christian period, in particular North Africa at Chlef and Djemila in Algeria, and Byzantium at Saint John Studio in Constantinople. Where Christian churches have been built over mithraea, the mithraeum has often been adapted to serve as a crypt.
The famous crypt at Old St. Peter's Basilica, Rome, developed about the year 600, as a means of affording pilgrims a view of Saint Peter's tomb, which lay, according to the Roman fashion, directly below the high altar. The tomb was made accessible through an underground passageway beneath the sanctuary, where pilgrims could enter at one stair, pass by the tomb and exit, without interrupting the clerical community's service at the altar directly above.