Friedrich Barbarossa arrives at Niš, the capital of Serbian King Stefan Nemanja, during the Third Crusade.

Frederick Barbarossa, also known as Frederick I, was the Holy Roman Emperor from 1155 until his death in 1190. He was elected King of Germany in Frankfurt on 4 March 1152 and crowned in Aachen on 9 March 1152. He was crowned King of Italy on 24 April 1155 in Pavia and emperor by Pope Adrian IV on 18 June 1155 in Rome. Two years later, the term sacrum ("holy") first appeared in a document in connection with his empire. He was later formally crowned King of Burgundy, at Arles on 30 June 1178. His nickname of Barbarossa "was first used by the Florentines only in 1298 to differentiate the emperor from his grandson, Frederick II ... and was never employed in medieval Germany". In German, he was known as Kaiser Rotbart, which in English means "Emperor Redbeard". The prevalence of the Italian nickname, even in later German usage, reflects the centrality of the Italian campaigns under his reign, and "remains to this day one of the [most] powerful historical monikers."

Niš, less often spelled in English as Nish, is the third largest city in Serbia and the administrative center of the Nišava District. It is located in the southern part of Serbia. According to the 2022 census, the city proper has a population of 178,976, while its administrative area has a population of 249,501 inhabitants.

The Kingdom of Serbia (Serbian: Краљевина Србија / Kraljevina Srbija, or the Serbian Kingdom, also known as Kingdom of Serbs ; Latin: Regnum Serbiæ; Greek: Βασίλειο της Σερβίας, also known by historical exonym Rascia, was a medieval Serbian kingdom in Southern Europe comprising most of what is today Serbia, Kosovo, and Montenegro, as well as southeastern Bosnia and Herzegovina, parts of coastal Croatia south of the Neretva river, Albania north of the Drin River, North Macedonia, and a small part of western Bulgaria. The medieval Kingdom of Serbia existed from 1217 to 1346 and was ruled by the Nemanjić dynasty. The Grand Principality of Serbia was elevated with the regal coronation of Stefan Nemanjić as king, after the reunification of Serbian lands. In 1219, the Serbian Orthodox Church was reorganized as an autocephalous archbishopric, headed by Saint Sava. The kingdom was proclaimed an empire in 1346, but kingship was not abolished as an institution, since the title of a king was used as an official designation for a co-ruler of the emperor.