City history
Established in the Red River Delta over a millennium ago, Hanoi evolved from the imperial citadel of Thăng Long into a modern metropolis operating on year-round Indochina Time.
Chapter one
Earliest documented name
"Song Peace"
Recorded in 5th-century Chinese dynastic chronicles, Tống Bình (Songping) served as an administrative seat in the Red River Delta around 454–456 CE. Because pre-Chinese indigenous names for the settlement were not recorded in surviving written records, Tống Bình represents the earliest documented historical name for the central Hanoi area.
Song Peace
Established as an administrative center during the Chinese Northern and Southern Dynasties, representing the earliest documented seat in central Hanoi.
Great Outer Citadel
Named when Tang Dynasty Governor Gao Pian constructed an expanded fortress along the Red River, which later served as the seat for local administrative rulers.
Ascending Dragon
Proclaimed by Emperor Lý Thái Tổ after reportedly seeing a golden dragon soar above the Red River, establishing the city as the capital of Đại Việt.
Eastern Capital
Renamed Đông Đô when the capital briefly shifted west, then Đông Kinh under the Lê Dynasty, which European traders transliterated as Tonkin.
Northern Citadel
Used during the early Nguyễn Dynasty when Emperor Gia Long moved the national capital south to Huế, reorganizing the northern territory under a regional governor.
Inside the Rivers
Officially assigned in 1831 by Emperor Minh Mạng during administrative reforms, describing the city's location enclosed by the Red and Đáy rivers.
Chapter two
French colonial authorities established mean solar time based on the Phủ Liễn Observatory meridian (UTC+07:06:30) for administration across Tonkin and French Indochina.
French Indochina standardized timekeeping to UTC+07:00 relative to Greenwich, aligning Hanoi and the region to 105° East longitude standard time.
Under Vichy French administration during World War II, standard time across Indochina shifted forward by one hour to UTC+08:00.
Occupying Japanese forces aligned local time to Tokyo Standard Time (UTC+09:00), which was reverted following the end of wartime control later that year.
The Democratic Republic of Vietnam in Hanoi officially adopted UTC+07:00 standard time by government decree, creating a one-hour offset difference with South Vietnam.
Following national reunification, UTC+07:00 (Indochina Time) was established as the unified, year-round standard time across all provinces of Vietnam.
Chapter three
Emperor Lý Thái Tổ issued the Edict on Transfer of Capital (Chiếu dời đô), relocating the royal court from Hoa Lư to Đại La and renaming it Thăng Long, establishing Hanoi as the political heart of Vietnam.
French colonial architects completed the Hanoi Post Office on the eastern shore of Hoàn Kiếm Lake, featuring a rooftop clock tower that became Hanoi's primary public timekeeper.
The opening of the Paul Doumer Bridge (now Long Biên Bridge) across the Red River integrated Hanoi into regional railway lines, making synchronized timetables essential for civil transit.
French scientists established Phủ Liễn Observatory in northern Vietnam to provide astronomical time measurements, telegraphic time signals, and meteorological forecasts for Tonkin.
Because Hanoi operated on UTC+07:00 following its 1967 reform while Saigon remained on UTC+08:00, the 1968 Lunar New Year fell on January 29 in North Vietnam and January 30 in South Vietnam.