Celts and Picts
 
The Celts settled in Britain around 500 BC
     
The Celts appear on the historical arena for the first time ca. 600 BC in the encounter with the Greeks, and later (400 BC) with the Romans. The People is described by contemporary historians, and the descriptions are of course colored by the fact that they constituted a barrier or threat to the “civilized” Empire builders of the day. They were regarded as uncultivated barbarians and portrayed in a disparaging fashion more...
Celts Buriel ritual
All about -The Celts
   
Blueprinting the Celts (BBC documentary link)

Romans never conquered the Northern Picts
Picts and Romans in Battle