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.
The Picts held their territory against the invading Romans in a number of engagements and, although they were defeated in battle, they won the war; Scotland holds the distinction of never falling to the invading armies of Rome, even though the Romans attempted conquest numerous times. The Picts exist in the written record from their first mention in 297 CE until c. 900 CE, when no further mention is made of them. As modern scholars point out, their absence from written history does not mean that they mysteriously vanished or were conquered by the Scots and annihilated; it simply means no more was written about them as they merged with the southern Scots culture, who already had a written history by that time, and the two histories became one from then on.