 The inhabitants had chosen to start living in the hill as a way of protection against attacks and looting by rival tribes.The migrations of Turduli and Celtici proceeding from the South of the Iberian Peninsula heading North were the reason for the improvement of the defensive systems of the castros around 500 BC.Cividade de Terroso is one of the most heavily defensive castros, given that the acropolis was surrounded by three rings of walls.