A crypt is a chamber, wholly or partly below ground, built beneath the chancel, apse or nave of a church, most often used historically for burial and for the safekeeping and display of relics. Because a crypt sits directly under the most sacred part of the building above it, typically the altar or the shrine of a saint, burial within it was traditionally considered especially prestigious, reserved for bishops, founders, major benefactors or the saint to whom the church itself was dedicated, so a crypt's occupants often tell historians a great deal about who a particular church community considered most significant across its history.
Architecturally a crypt is usually a lower, more compressed space than the church above it, frequently vaulted on stouter, closer-set columns needed to support the greater weight of the structure overhead, giving many crypts a noticeably different, heavier and more intimate character than the taller, more open nave they sit beneath. Where a crypt houses a venerated relic or tomb, it is often reached by its own separate stair from the main church, sometimes designed to let visiting pilgrims descend, view the tomb or relic, and exit without disrupting services taking place in the church above, a circulation solution serving much the same purpose underground that the ambulatory serves at ground level.