The popular FPS/tower-defense hybrid Sanctum will be receiving a sequel in 2013, according to Joystiq. After launching on Steam last April, Sanctum became an indie success story, quickly selling more than 300,000 units. The game took the typical tower-defense formula and injected it with more than a few ampules of adrenaline. In four-player co-op, players have to carefully construct and upgrade their defenses to stop waves of monsters, before leaping into the fray with their own upgradable weapons. No details are available on what new features await players in Sanctum 2, except that PSN and Xbox Live players will also get to experience the teamwork.