On 18 June 1155, Frederick I Barbarossa ⓘ was crowned Holy Roman Emperor in Rome by Pope Adrian IV ⓘ. The ceremony formally confirmed Frederick’s transition from King of the Romans (elected in 1152) to emperor, reviving the imperial dignity associated with Charlemagne ⓘ and the Roman tradition of universal Christian sovereignty.

Frederick had crossed the Alps in 1154 to secure imperial coronation and to assert imperial rights in northern Italy. His arrival in Rome occurred amid political tension: the city was unstable, influenced by republican agitation associated with Arnold of Brescia, and relations between papacy and empire remained cautious after decades of conflict over investiture and jurisdiction.

The coronation itself was both liturgical and political. By receiving the imperial crown from the pope, Frederick affirmed the medieval conception that imperial authority, while universal in scope, was sacral and ceremonially conferred within the Roman Church. At the same time, the event reinforced imperial claims to oversight in Italy, including rights over communes and episcopal territories.

In the years following his coronation, Frederick sought to reassert imperial jurisdiction in northern Italy, leading to confrontation with the Lombard communes and ultimately to the formation of the Lombard League ⓘ (1167). His defeat at the Battle of Legnano (1176) would temper those ambitions, but the coronation of 1155 marked the high point of his early imperial authority.

The event stands as a pivotal moment in the twelfth-century redefinition of sovereignty in Latin Christendom, balancing papal sacral legitimacy with imperial claims to universal rule.