The front page of English Wikipedia gets around five million hits per day. Highlighted sections of the page, such as “Did you know” and “In the news” trumpet the site’s purpose: sharing knowledge for its own sake. One of these sections, “On this day…” features five different facts each day, with links to relevant articles. These facts in turn are chosen from a large collection of roughly 100 historic events for each date. Many other language versions of Wikipedia have a similar “This day in history” section, though with different sets of facts.

As with everything else on Wikipedia, this collection of historic facts is offered freely for anyone to use for any purpose. “On this day in history” facts are ideal for sharing on social media, for example by Wikipedia’s official presence on Twitter.

Napoléon Bonaparte, listed in Wikipedia’s May 26 article for his coronation as King of Italy on 26 May 1805. Image from the Curzon Collection of political prints, CC-BY the Bodleian Libraries.

To avoid repetition from year to year, it helps to be able to draw on a large pool of historic events, so each day can showcase a variety of types of event, of locations and of eras. There is a relative shortage of events before 1800, so additions are welcome.

Being featured on the front page generates a lot of interest in the article.

• The Alhambra Decree article typically gets about 300 views per day. When linked from the front page as a recent “On this day” item, it had nearly 10,000.
• The Treaty of Fontainebleau (1814) article gets 70 to 80 views on a typical day, but had 5,400 when linked from the home page on its anniversary.
• The article about Suvarnadurg, an Indian fort, usually gets around 30 views a day, but had 8,500 when the fort’s 1755 capture by the East India Company was listed on April 2.

By considering one example, we can look at how a historic event is made visible in Wikipedia.

March 31: 1492 – The Catholic Monarchs of Spain issued the Alhambra Decree, ordering all Jews to convert to Christianity or be expelled from the country.

The typical form is a single sentence, in past tense, linking multiple different Wikipedia articles, with a bold link to the one most closely connected to the fact. Not every historical event qualifies:

• The event must have happened on a single day, so not a crisis or war, but a precipitating or concluding event such as the signing of a treaty.
• Births and deaths have their own process for appearing on the front page, so do not qualify for this collection of facts.
• It must be an event with notable repercussions: one notable figure marrying another, or writing a letter to another, is not always significant in itself, but can be significant by initiating other events.
• There must be no controversy about the day on which it happened. Reputable sources should agree.
• The fact must be backed up by at least one reliable source, which must be cited in the article. As with all Wikipedia references, paywalled sources are fine but open-access sources have an advantage because they can be checked by Wikipedians outside subscribing institutions. With software developments over the last couple of years, adding citations has become extremely easy: the Cite tool expands DOIs into full citations and normally succeeds in transforming web links into full citations.

If you have a cited fact that meets the above criteria, it can have multiple mentions in Wikipedia:

• The fact must be stated in the “home” article, in this case Alhambra Decree.
• It can also go in the articles about the calendar date and the year. There are English Wikipedia articles about the year 1492 and about the date March 31. Unlike most Wikipedia articles, these are essentially lists of facts under different headings.
• It can also appear in the biographies of the people, organisations or nations involved (in this case, Isabella of Castille). Some topics have timeline articles which are essentially lists of dates, such as Timeline of Spanish history.

The articles about individual dates, such as March 30, also have lists of births and deaths. In the long term, these will probably be driven by Wikidata, which is ideal for this kind of data. These lists have the same relative paucity of dates before 1800, and the same requirement that dates should be sourced and uncontroversial.

Facts for a particular day are chosen well in advance by an administrator, working behind the scenes in an area called the Selected anniversaries project. It is accepted, even encouraged, for other users to proactively edit in their own suggestions if they know wiki-code. The listing is decided two to four days in advance, so include your suggestion further in advance than that.

The guidelines give preference to events with a significant anniversary (meaning a multiple of 25, e.g. a 325th anniversary), events that differ from the others on the list (in era or geography), and articles that have not been on the front page before. “On this day” articles do not have to be comprehensive, but should be good examples of Wikipedia articles with citations in all sections. Each day’s “staging area” has a list of events that were submitted but did not qualify. Usually the article is rejected for having insufficient citations, so by improving the articles with links to scholarly sources, we can help those links reach the front page.

So there is an opportunity here for heritage organisations and historians to extend awareness of the turning points of history, and the use of biographical papers or databases. We just need to succinctly describe the key events and share citations about them.

—Martin Poulter, Wikimedian in Residence

This post licensed under a CC-BY-SA 4.0 license