Looking at maps of the Roman Empire, I noticed how there is a legion based in North-Western Spain. What was the purpose in maintaining such a legion in that area? I understand that mines were in place in such region but is that the sole reason?
Hispania Tarraconensis, the northern portion of the Iberian peninsula, was not fully conquered until around 19 BC, after a decade long war involving eight legions. Two of those would be drawn off for the conquest of Germania (I Germanica and V Alaudae), and a couple for the revolt in Pannonia, and another to reinforce the Rhine after the disaster at Teutoburg. That left three legions to occupy Hispania (IIII Macedonica, VI Victrix, and X Gemina) and deal with any remaining resistance for the next several decades.