This paper analyzes the twentieth-century political philosopher Eric Voegelin's Gnosis-thesis put forth in The New Science of Politics, focusing particularly on his treatment of the medieval abbot and theologian, Joachim of Fiore. It explores Joachim's life, works, and connection to three symbols designated by Voegelin as being central to Western political thought: the Third Realm, the Brotherhood, and the Last Leader. While these concepts had been around before Joachim's time, the repeated association between them and the abbot's works and pseudo-prophecies based on his works significantly influenced European politics for decades to come. Joachim is more correctly categorized as an apocalyptic thinker than a Gnostic one, but Voegelin was right to position the abbot as a liminal figure in Western politics and history.