The German Emperor. He receives the title from Dalmatia, Croatia, and the line of the Danube, which, by the arrangement of Diocletian, was governed by a prince entitled Caesar of the Holy Roman Empire, as successor of the emperor of the old Roman empire. It was Albert II., Duke of Austria, who added the Holy Roman Empire to the imperial throne in 1438; and William I., king of Prussia, on being crowned German emperor in 1871, took the title.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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