San Marino

City · 301 CE · in Europe

Capital of Republic of San Marino (1797–1799).

Linfen (c. 306 CE): Capital of Former Zhao (306–329).
Kanchipuram (c. 283 CE): Capital of Late Pallava Empire (283–805).
Al-Hirah (c. 270–602 CE): Capital of Lakhmid Kingdom (270–602).
Ye (c. 337–576 CE): Capital of Later Zhao (337–351), Northern Qi (555–576).
Ji (c. 337 CE): Capital of Former Yan (337–370).
Jeju (c. 263 CE): Capital of Tamna (263–1278).
Cologne (c. 261 CE): Capital of Gallic Empire (261–274).
Palmyra (c. 261–1929 CE): Capital of Palmyrene Empire (261–269).
Washim (c. 260 CE): Capital of Vakataka Kingdom (260–500).
Wiryeseong (c. 347 CE): Capital of Baekje (347–660).

Around the same time and place

Constantine the Great (c. 272 CE – 337 CE): First Roman emperor to convert to Christianity; he legalised the faith and refounded Byzantium as Constantinople.
Edict of Milan (313 CE): Agreement between the emperors Constantine and Licinius granting religious tolerance to Christians throughout the Roman Empire.
First Council of Nicaea (325 CE): The first ecumenical council of the Christian church, convened by Constantine the Great, condemned Arianism and adopted the Nicene Creed.
Constantinople (330 CE): Constantine the Great refounded Byzantium as Constantinople, capital of the Roman Empire in the east; as Istanbul it later became the Ottoman capital.
Statue of Zeus at Olympia (c. 435 BCE – c. 425 CE): Giant gold-and-ivory seated statue of Zeus by Phidias in his temple at Olympia, one of the Seven Wonders of the Ancient World; lost in the fifth century CE.
Praetorian Guard (27 BCE – 312 CE): Augustus organised the Praetorian Guard in 27 BCE as the bodyguard of the Roman emperors. The guard came to make and unmake emperors, and Constantine the Great disbanded it in 312.
Trier (16 BCE – 1618 CE): Capital of Electorate of Trier (1333–1618).
Battle of the Milvian Bridge (312 CE): Constantine defeated his rival Maxentius outside Rome, a victory he attributed to the Christian God.