A Pictish stone is a type of monumental stele, generally carved or incised with symbols or designs. A few have ogham inscriptions. Located in Scotland, mostly north of the Clyde-Forth line and on the Eastern side of the country, these stones are the most visible remaining evidence of the Picts and are thought to date from the 6th to 9th century, a period during which the Picts became Christianized. The earlier stones have no parallels from the rest of the British Isles, but the later forms are variations within a wider Insular tradition of monumental stones such as high crosses. About 350 objects classified as Pictish stones have survived, the earlier examples of which hold by far the greatest number of surviving examples of the mysterious Pictish symbols, which have long intrigued scholars.