Brunswick

City · 861 CE · in Europe

Capital of Duchy of Brunswick (1815–1870).

Zaranj (c. 861 CE): Capital of Saffarid Dynasty (861–899).
Sibenik (860 CE): Capital of Kingdom of Croatia (926–1098).
Beiting (c. 860–1138 CE): Capital of Qocho Kingdom (860–1138).
Smolensk (863 CE): Capital of Principality of Smolensk (1056–1406).
Olbia (c. 866 CE): Capital of Giudicato of Gallura (866–1209).
Amol (c. 866 CE): Capital of Zaydi Alid dynasties (866–928), Ziyarid dynasty (936–979).
Porto Torres (c. 866 CE): Capital of Giudicato of Logudoro (866–1259).
La Seu d'Urgell (c. 870 CE): Capital of County of Urgell (870–1413).
Kashgar (c. 850 CE): Capital of Kara-Khanids (850–1045), Eastern Kara-Khanids (1046–1138), Western Karakhanid Khanate (1046–1084), and 4 more.
Palermo (c. 850 CE): Capital of Emirate of Sicily (850–1091), Kingdom of Sicily (1139–1266), Kingdom of the Two Sicilies (1815–1860).

Around the same time and place

Charlemagne (c. 747 CE – 814 CE): King of the Franks who conquered much of Western Europe, was crowned emperor in 800 and promoted a revival of learning, the Carolingian Renaissance.
Founding of Kievan Rus' (882 CE): Oleg of Novgorod took Kyiv and made it his capital, creating the state of Kievan Rus', which united East Slavic lands under the Rurik dynasty.
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.
Nitra (c. 814 CE): Capital of Principality of Nitra (814–839).
Jaca (c. 830 CE): Capital of County of Aragon (830–921).
Treaty of Verdun (843 CE): Treaty dividing the Carolingian Empire among three grandsons of Charlemagne, roughly foreshadowing France, Germany and Italy.
Alfred the Great (849 CE – 899 CE): King of Wessex who defended his kingdom against the Vikings, reorganised its defences and promoted learning in English.