The Pillar of Autumn is a heavily modified United Nations Space Command Halcyon-class cruiser in the Halo: Combat Evolved video game, often abbreviated as "POA".

Before the war with the Covenant, the Pillar of Autumn was set to be decomissioned. The Halcyon-class cruiser was poorly regarded by UNSC officers and crewmen and considered to be too lightly armed and armoured for its role. After being refitted, the Pillar of Autumn was one of the most powerful ships in the UNSC fleet. Modifications to the ship included reinforced armor, increased missile capacity, an improved Shaw-Fujikawa engine, and a Magnetic Accelerator Cannon capable of firing three "shredder shots" on a single charge.

The Pillar of Autumn was one of few ships to escape the Covenant armada following the fall of the planet Reach. The ship made a slipstream jump to the planet Threshold, location of Forerunner Installation 04, which the The Covenant believed was their religious icon "Halo." The ship's crew believed the jump to be random, in order to avoid leading the Covenant to Earth as per the Cole Protocol; in actuality the shipboard AI, Cortana, interpreted symbols on an alien artifact into map coordinates.

Covenant starships intercepted the Pillar of Autumn upon its arrival at Threshold. Reluctant to use their more powerful weapons for fear of causing collateral damage to "Halo," the Covenant armada attacked with relatively light fire in coordination with numerous boarding craft filled with assault troops. The boarding parties were charged with retrieving senior officers, including the commanding officer Captain Jacob Keyes, for interrogation.

Keyes and the rest of the command staff managed to crash the ship on the surface of "Halo," and surviving Marines quickly formed a formidable resistance movement. After 343 Guilty Spark's true intentions were revealed, Cortana and the Master Chief manually detonated the ship's nuclear fusion engines in order to destroy "Halo," preventing the escape of Flood and Covenant forces as well as the massive destruction Halo's activation would have wrought.