The triptych form appears in early Christian art, and was a popular standard format for altar paintings from the Middle Ages onwards. Its geographical range was from the eastern Byzantine churches to the Celtic churches in the west. During the Byzantine period, triptychs were often used for private devotional use, along with other relics such as icons. Renaissance painters such as Hans Memling and Hieronymus Bosch used the form. Sculptors also used it. Triptych forms also allow ease of transport.