Jeju

City · c. 263 CE · in Central Asia

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).
Al-Hirah (c. 270–602 CE): Capital of Lakhmid Kingdom (270–602).
Kanchipuram (c. 283 CE): Capital of Late Pallava Empire (283–805).
San Marino (301 CE): Capital of Republic of San Marino (1797–1799).
Luoyang (c. 224 CE): Capital of Cao Wei (224–264), Western Jin (266–420), Eastern Wei (534–550), and 1 more.
Linfen (c. 306 CE): Capital of Former Zhao (306–329).
Ezhou (c. 207 CE): Capital of Eastern Wu (207–229).
Vijaya (c. 207 CE): Capital of Chámpa (207–1652).

Around the same time and place

Three Kingdoms period (220–280 CE): After the end of the Han, China was divided among the states of Wei, Shu and Wu.
Yayoi period (c. 300 BCE – c. 300 CE): Era when wet-rice farming and metalworking spread to Japan from the continent; the Yoshinogari site is a major settlement.
Silla (c. 57 BCE – c. 935 CE): Kingdom with its capital at Gyeongju, traditionally founded in 57 BCE, that unified most of Korea in the 7th century.
Goguryeo (c. 37 BCE – c. 668 CE): Kingdom traditionally founded by Jumong in 37 BCE that grew to rule northern Korea and Manchuria.
Baekje (c. 18 BCE – c. 660 CE): Kingdom in southwestern Korea, traditionally founded in 18 BCE, a conduit of culture and Buddhism to Japan.
Cao Cao (155 CE – 220 CE): Warlord and chancellor of the late Han who unified northern China; his son founded the state of Wei.
Kofun period (c. 250–538 CE): Era named for huge keyhole-shaped burial mounds such as the Daisen Kofun, reflecting the rise of the Yamato state.
Wang Xizhi (303 CE – 361 CE): Calligrapher of the Eastern Jin, revered as the "Sage of Calligraphy".