By 1860, improvements in artillery, particularly the replacement of the bronze cannon with steel, rifled guns firing pointed, exploding, shells gave the opportunity for accurate fire over much longer ranges. Typical guns at the time could hit targets 8–9 km away. The decision was made to create extra batteries above the Fort Supérieur — the Batterie des Caurres and the Batterie de Serre de l’Aut. These gave a much better firing line for engaging targets earlier in their approach over the cols and with the Observatoire de Serre de l’Aut at the top of the mountain meant that the fort was able to secure the valley in a very efficient manner.