Subterranean chamber, usually under a church floor. The catacombs of the early Christians were known as cryptae, and when churches came to be built over the tombs of saints and martyrs, subterranean chapels were built around the actual tomb. As early as the reign of Constantine I (AD 306–37), the crypt was considered a normal part of a church. Later its size was increased to include the entire space beneath the choir or chancel; the crypt of Canterbury Cathedral is an elaborate underground church with its own apse. Many secular medieval European buildings also had richly decorated crypts.