The artillery, and especially the cannons and mortars, were the most powerful long range weapons upon which the fortifications relied. In general, all the artillery fell within two categories; mortars and cannons. The mortars were designed to fire the largest and heaviest of projectiles in a curved trajectory. They could fire over the tops of fortifications and high obstacles. The cannons fired their shots on a straight trajectory and their effectiveness depended on the weight of the projectile. The heavier the shot, the more damage it would caused. The earlier artillery pieces were made from cast iron but it later became possible to cast them in bronze from a single mold, making them more effective. Each of the Spanish cannons were given a name and a record was kept to identify its location. The cannons were classified by the weight of the ball or shell that they fired. A twelve pounder cannon fired a shot weighing 12 pounds. The type of projectiles varied considerably; there were solid cannon balls, canister shot, grape shot (many small grape-like balls fired together) and hot shots (cannon balls heated until red hot). Six soldiers were needed to fire a cannon.