Pictish symbol stones are a unique class of sculptured monument of the Pictish people in the Post-Roman period. The Picts occupied Scotland north of the Forth and possessed a distinctive culture, seen particularly in their carved symbol stones. The stones are roughly divided into three chronological categories. The Class I stones (5th-7th century) are rough-hewn, undressed blocks or pillars, inscribed with pictorial symbols of spiral creatures, such as fishes and birds. They are also decorated with strange geometric shapes as well as inanimate objects like mirrors and combs, grouped together in various combinations. Class II (8th-10th century) stones are regularly dressed slabs which the same range of carvings but with the addition of new Christian elements and humans in animated scenes. Class III stones (from 9th century) are, in most cases, free-standing crosses decorated with a combination of a distinctive form of interlace as well as some elements of the older motifs. Some bear Ogham inscriptions from which it has recently been shown that three languages were in use, two Celtic and one pre-Indo-European. From these memorial stones, we know something of the Pictish royal succession.