The Celts are an ancient people scattered across Europe that have in common the Celtic languages. The Romans write of Celtic priests, known as druids, that carry out mysterious rites and sacrifices. The Wickerman in Gaul is such an example where humans are sacrificied in a wooden statue. But the Celts are mainly known for their beautiful style of decoration. It is characterized by the use of spirals, knots, and triskeles. Irish Christian monks are also the first to perfect the art of illumination. The most beautiful examples are the 7th-century Book of Kells and the Lindisfarne Gospels, also know as the Book of Durham.