Esztergom

City · c. 900 CE · in Europe

Capital of Principality of Hungary (900–999), Kingdom of Hungary (1001–1256).

Székesfehérvár (c. 900 CE): Capital of Principality of Hungary (900–999), Kingdom of Hungary (1000–1543).
Andorra la Vella (900 CE): Capital of Principality of Andorra (1815–today).
Benabarre (c. 900 CE): Capital of County of Ribagorza (900–1084).
Roda de Isábena (c. 900 CE): Capital of County of Ribagorza (900–1084).
Maragheh (c. 898 CE): Capital of Sajid Dynasty (898–929), Ilkhanate (1294–1335).
Pskov (903 CE): Capital of Pskov Republic (1348–1510).
Bratislava (907 CE): Capital of Kingdom of Hungary (1526–1546).
Jeonju (c. 892 CE): Capital of Hubaekje (892–935).
Kaesong (c. 911 CE): Capital of Taebong (911–918), Goryeo (922–1392).
Lugo (c. 911 CE): Capital of Kingdom of Galicia (911–1125).

Around the same time and place

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.
Cyrillic script (c. 893 CE): Scholars in the First Bulgarian Empire, probably at Preslav, built a Slavic alphabet mainly from Greek letters; Cyrillic now writes Russian, Ukrainian, Bulgarian, Serbian and many more.
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.
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.
Palermo (c. 850 CE): Capital of Emirate of Sicily (850–1091), Kingdom of Sicily (1139–1266), Kingdom of the Two Sicilies (1815–1860).
Sibenik (860 CE): Capital of Kingdom of Croatia (926–1098).
Brunswick (861 CE): Capital of Duchy of Brunswick (1815–1870).