sentences:  These probably developed from earlier traditions using wood, perhaps with metalwork attachments, and earlier pagan Celtic memorial stones; the Pictish stones of Scotland may also have influenced the form.The earliest surviving examples seem to come from the territory of the Anglo-Saxon kingdom of Northumbria, which had been converted to Christianity by Irish missionaries; it remains unclear whether the form first developed in Ireland or Britain.Their relief decoration is a mixture of religious figures and sections of decoration such as knotwork, interlace and in Britain vine-scrolls, all in the styles also found in insular art in other media such as illuminated manuscripts and metalwork.