Stockholm

City · c. 980 CE · in Europe

Capital of Kingdom of Sweden (980–today), Kalmar Union (1436–1523), Swedish Empire (1612–1721), and 1 more.

Vitebsk (974 CE): Capital of Principality of Vitebsk (1111–1187).
Besalú (c. 988 CE): Capital of County of Besalú (988–989).
Bruges (c. 990 CE): Capital of County of Flanders (990–1384).
Le Mans (c. 990 CE): Capital of County of Maine (990–1481).
Blois (c. 990 CE): Capital of County of Blôis (990–1401).
Rodez (c. 990 CE): Capital of County of Rouergue (990–1065).
Vladimir (990 CE): Capital of Principality of Rostov-Suzdal (1125–1240), Principality of Vladimir-Suzdal (1294–1389).
Vic (c. 990 CE): Capital of County of Osona (990–1110).
Copenhagen (c. 965 CE): Capital of Kingdom of Denmark (965–1406), Kalmar Union (1443–1523), Denmark-Norway (1536–1814).
Luxembourg (963 CE): Capital of Duchy of Luxembourg (1429–1449).

Around the same time and place

Christianization of Kievan Rus' (988 CE): Vladimir the Great adopted Orthodox Christianity from Byzantium and had the people of Kyiv baptised in the Dnieper.
Trier (16 BCE – 1618 CE): Capital of Electorate of Trier (1333–1618).
Varangians to the Greeks (c. 800–1100 CE): Scandinavian traders and warriors travelled from the Baltic up the Neva and Volkhov past Novgorod, portaged to the Dnieper and sailed down past Kiev to the Black Sea and Constantinople.
Otto the Great (912 CE – 973 CE): German king who defeated the Magyars and was crowned emperor in Rome in 962; he was buried in Magdeburg.
Baptism of Poland (966 CE): Duke Mieszko I accepted baptism, bringing Poland into Latin Christendom; the event is traditionally seen as the founding of the Polish state.
Stephen I of Hungary (c. 975 CE – 1038 CE): First king of Hungary, crowned in 1000 or 1001, who converted his people to Christianity; venerated as Saint Stephen.
Gdańsk (997 CE): Capital of Free City of Danzig (1920–1939).
Beowulf (c. 1000 CE): Old English epic poem about the hero Beowulf, surviving in a single manuscript from around 1000; the most important work of Old English literature.