Regensburg

City · c. 911 CE · in Europe

Capital of Kingdom of Germany (911–961), Holy Roman Empire (1594–1806), Holy Roman Empire Minor States (1594–1806), and 1 more.

Kaesong (c. 911 CE): Capital of Taebong (911–918), Goryeo (922–1392).
Lugo (c. 911 CE): Capital of Kingdom of Galicia (911–1125).
Changsha (c. 911 CE): Capital of Southern Chu (911–951).
Hangzhou (c. 911 CE): Capital of Wuyue (911–978).
Beijing (c. 911 CE): Capital of Yan Kingdom (911–914), Ming Dynasty (1375–1644), Empire of China (1916–1916), and 2 more.
Mahdia (c. 911 CE): Capital of Fatimid Caliphate (911–948), Zirid dynasty (1057–1148), Kingdom of Africa (1152–1160).
Tui (c. 911 CE): Capital of Kingdom of Galicia (911–1125).
Fengxiang District (c. 911 CE): Capital of Qi Kingdom (911–924).
Bratislava (907 CE): Capital of Kingdom of Hungary (1526–1546).
Shangjing Linhuangfu (c. 916 CE): Capital of Liao Dynasty (916–1125).

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.
Brunswick (861 CE): Capital of Duchy of Brunswick (1815–1870).
Mission of Cyril and Methodius (863 CE): Byzantine brothers sent as missionaries to Great Moravia, who created the Glagolitic alphabet and translated the liturgy into Old Church Slavonic.
Great Heathen Army (865–878 CE): A large coalition of Scandinavian warriors landed in East Anglia in 865, took York, and conquered Northumbria, East Anglia and much of Mercia before Alfred the Great defeated Guthrum at Edington in 878.