What happened on September 21

53 documented historical events happened on September 21, from antiquity to the present day. The best known is this: Norman invasion of Ireland: English and Irish forces conquered Dublin, forcing Ascall mac Ragnaill, the last Norse–Gaelic king of Dublin, into exile. On the same day, in another year: The Treaty of Arras is promulgated, causing Burgundy to switch sides in the Hundred Years' War. On Almanaccolo every event is listed in chronological order, grouped by century, and links to the Wikipedia article it comes from, so you can always read further or check the source. Alongside the events you find who was born and who died on this date, and which observances are celebrated around the world.

160 people with a Wikipedia article were born on September 21, including Bruce Arena, Aslan Maskhadov, Dave Gregory (musician). The list spans every era and every field — art, science, politics, sport, entertainment — ordered by year of birth, from the earliest to the most recent. The six featured people are those most has been written about: the ordering uses the length of their Wikipedia article as an indicator of prominence. For each one you find their occupation, year of birth and a link to the full biography.

100 people with a Wikipedia article died on September 21, including Virgil, Flavius Aetius, Pope Conon. The list is in chronological order by year of death and spans all of documented history, from antiquity to the present day. For each person you find their occupation, the year and a link to the Wikipedia biography, where the full story and its sources can be read.

18 observances are celebrated on September 21 around the world: Autumnal equinox observances in the Northern Hemisphere, vernal equinox observances in the Southern Hemisphere (see September 22): Spring Day (Argentina), Christian feast day: Cadoc, Christian feast day: Ephigenia of Ethiopia, Christian feast day: Laurent-Joseph-Marius Imbert (one of the Korean Martyrs), Christian feast day: Matthew the Evangelist (Western Church), Christian feast day: Maura of Troyes. The list gathers national holidays, international days and religious or civil observances falling on this date in different countries, as recorded on Wikipedia. Some are fixed and recur on the same day every year; others depend on the local calendar. Each links to the article explaining its origin and meaning.