Note: This is part three of a four-part series. The rest of the series can be found here.
"The Picts were a people of northern Scotland who are defined as a 'confederation of tribal units whose political motivations derived from a need to ally against common enemies' ... They were not a single tribe, nor necessarily a single people, although it is thought that they came originally from Scandinavia as a cohesive group. Since they left no written record of their history, what is known of them comes from later Roman and Scottish writers and from images the Picts themselves carved on stones. They are first mentioned as 'Picts' by the Roman writer Eumenius in 297 CE, who referred to the tribes of Northern Britain as 'Picti' ('the painted ones'), ostensibly because of their habit of painting their bodies with dye. This origin of their name has been contested by modern scholarship, however, and it is probable they referred to themselves as some form of 'Pecht', the word for 'the ancestors'. They were referenced earlier by Tacitus who referred to them as 'Caledonians' which was the name of only one tribe." Source: Ancient History Encyclopedia.
Related: Pictish carved stones in Scotland.