baptistery (băpˈtĭstrē) [key], part of a church, or a separate building in connection with it, used for administering baptism. In the earliest examples it was merely a basin or pool set into the floor. Later, the Christian Church set aside a separate structure for the ceremony. The earliest such structure still extant is in the Lateran basilica at Rome, in which, by tradition, Emperor Constantine was baptized (337). Octagonal in plan, it formed a model for many subsequent baptisteries, most of which were octagonal or circular. In the center of the chamber was the sunken pool, often surrounded by columns, with curtains to screen the neophyte during immersion. Early baptisteries are chiefly found in Italy and Asia Minor. In Hagia Sophia there is a 6th-century example still extant. When immersion was no longer practiced, a separate structure became unnecessary and was supplanted by a place within the church itself, set aside for the purpose. The standing fonts of the Middle Ages and the Renaissance were often objects of superb artistry. In Italy separate baptisteries continued to be built in the 12th to the 15th cent., notably the beautiful Romanesque structures at Florence, Pisa, Siena, and Parma. For the baptistery at Florence Andrea Pisano and Lorenzo Ghiberti designed celebrated bronze doors; for that at Pisa Nicola Pisano carved the marble pulpit.