Roughly four and a half centuries separated the two empires, both of which were comprised of vast regions of western and central Europe. The Roman Empire was established in 27 B.C., when Augustus (also known as Octavian; 63 B.C.–A.D. 14), the grandnephew, adopted son, and chosen heir of Julius Caesar (100–44 B.C.), became emperor. His reign lasted until A.D. 476, when Rome fell to Germanic tribes.

The Holy Roman Empire (H.R.E.) began in the mid-900s A.D., when Otto I (912–973) of Germany gained control of most of northern and central Italy. Pope John XII (c. 937–964) crowned Otto emperor in 962. In the 1200s the area of power officially became known as the Holy Roman Empire. The H.R.E. was dismantled July 12, 1806, in the Confederation of the Rhine, which brought most of the German states under French domination—the result of the Napoleonic wars. But even after Napoleon Bonaparte (1769–1821) was permanently ousted as head of France in 1815, there were no attempts to reinstate the Holy Roman Empire.