In the earliest days of the nascent Imperium, civil war rocked the very foundations of humanity. The Emperor’s greatest son, Horus, His Warmaster in the Great Crusade that was meant to unite humanity, turned his back on his father to incite rebellion, and a conflict like no other engulfed the galaxy. Brother fought brother and warring demigod primarchs clashed across the stars. Hope failed, despair reigned, and the gods of Chaos rose to prominence. This was an age of darkness. This was the Horus Heresy.