Sacrum imperium is a phrase that first appears in the imperial chancery in a document of Frederick Barbarossa in 1157. It later developed into the title Holy Roman Empire (of the German nation), the name of Europe's largest polity for many centuries. Where other country names were based on the peoples inhabiting them, the Empire's name is of unknown provenance, though it obviously imitates the Roman Empire. I intend to survey the extant theories on its origin and meaning and show how 20th-century national discourse affected scholarly opinion. It is maintained that sacrum imperium was introduced by Rainald of Dassel to resacralise the Empire after the imperial defeat in the Investiture Controversy. Many opinions were based on this (1) that sacrum imperium means that the state is holier than the Church, (2) that Charlemagne's canonisation was a thinly veiled canonisation of the Empire, and (3) that Rainald of Dassel translated the three kings to Cologne to prove that there was no intermediary between the emperor and God. I will show that these views are derived from Zeumer's 1910 modelling of Rainald of Dassel after Otto von Bismarck and his 1872 Reichstag speech against Pope Pius IX.