Olomouc is said to occupy the site of a Roman fort founded in the imperial period, the original name of which, Iuliomontium (Mount Julius), would have been gradually corrupted to the present form. Although this account is not documented except as oral history, archaeological excavations close to the city have revealed the remains of a Roman military camp dating from the time of the Marcoman Wars.
During the 6th century, Slavs migrated into the area. As early as the 7th century, a centre of political power developed in the present-day quarter of Povel (situated in lowland, southerly from the city centre). Around 810 the local Slavonic ruler was defeated by troops of Great Moravian rulers and the settlement in Olomouc-Povel was destroyed.
A new centre, where the Great Moravian governor resided, developed at the gord at Předhradí, a quarter of the inner city (the eastern, smaller part of the medieval centre). This settlement survived the defeat of the Great Moravia (c. 907) and later gradually became the capital of the province of Moravia.
In 906 the first Jews settled in Olomouc. In 1060 they were forced into a ghetto and instructed to wear a yellow badge.
The bishopric of Olomouc was founded in 1063; centuries later in 1777, it was raised to the rank of an archbishopric. The bishopric was moved from the church of St. Peter (since destroyed) to the church of St Wenceslas in 1141 (the date is still disputed, other suggestions are 1131, 1134) under bishop Henry Zdík. The bishop's palace was built in the Romanesque architectural style. The bishopric acquired large tracts of land, especially in northern Moravia, and was one of the richest in the area.
Olomouc became one of the most important settlements in Moravia and a seat of the Přemyslid government and one of the appanage princes. In 1306 King Wenceslas III stopped here on his way to Poland. He was going to fight Wladislaus I the Elbow-high to claim his rights to the Polish
