Halo: Combat Evolved is a first person shooter that takes place on a mysterious planet-like construct referred to as 'Halo'. Two days before the story begins, the Covenant, a collection of alien species committed to the destruction of the human race, launch an assault on the home of Human military production, Reach, destroying it. A single starship, the Pillar of Autumn, survives the alien onslaught, carrying one of the last known SPARTANs- the "Master Chief". The ship initiates a random jump to Slipspace, hoping to lead the enemy away from Earth. Following coordinates chosen by the on board Al construct named 'Cortana', they jump to an alien built ring which orbits a planet. This ring is called Halo. Halo was built by a mysterious group of people in the distant past called "The Forerunners". Although the Protagonist (the Master Chief) does not know it, seven rings were constructed to completely eradicate all life in the galaxy. The rings were built as weapons of last resort to stop a parasitic race called "The Flood". Most of the history between the Forerunners and the Flood is unknown, but it appears that the Forerunners were overwhelmed by the Flood, who then proceeded to destroy their own civilization in an attempt to starve the flood, leaving the universe empty and safe for new organisms to evolve. The Covenant discovered the rings and believe that they will lead their civilization on a "Great Journey". The "Sacred Rings" are the most treasured artifacts of the Covenant and they guard the rings savagely. Each "Halo" requires an Index to activate. The player is to stop the Covenant from activating Halo and prevent the Flood spreading across the universe, while faced with a massive four way war fought over immense and beautiful landscapes.