The importance of Baptism as a rite of passage for entrants to the Christian church is such that architectural provision has been made for it since at least the first half of the third century CE , when, in Dura-Europos on the Euphrates River, a canopied bath-like structure was built in a house that was converted for use as a place of Christian worship. Later, separate buildings made for the ceremony of baptism are circular, square, or (most often) octagonal domed structures covering a font—usually a pool recessed into the center of the floor, fed either by a spring or by water piped from a cistern; there is usually an entrance chamber, or narthex, to one side. Baptisteries of this type were built alongside churches across the empire in the fifth and sixth centuries: examples include the baptisteries of St. John Lateran, Rome (440), Qal'at Sem'an (after 459), and Hagia Sophia in Constantinople (532), the latter made into an Ottoman tomb in the seventeenth century. Baptisteries could be…