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Year 1184 (MCLXXXIV) was a leap year starting on Sunday (link will display the full calendar) of the Julian calendar.
- Yaqub al-Mansur becomes the third Almohad Caliph.
- The warlord Ali b. Ghaniya and his brother Yahya seize by surprise the Almohad-dominated cities of Constantine, Béjaïa and Algiers. While they are away from their base in Mallorca, one of their brothers, Muhammad, takes control of the island and calls in the Almohads, whom intend to capture Mallorca for themselves. The Banu Ghaniya reenforcement arrives just in time from Africa, to defeat the Almohads and reassert their domination of the island.
- June 15 – Battle of Fimreite: King Sverre of Norway defeats and kills his rival, Magnus Erlingsson, to take the throne.
- The Almohads reconquer the Alentejo (except for Évora), and besiege Lisbon on land and blockade the port with their navy. A Portuguese soldier manages to swim to the largest ship of the fleet, and to sink it. This ship was so tall, it would have allowed the Muslims to easily reach the walls of the city. The next day, the Almohads have to retreat, taking with them a number of civilian captives. The Almohad army continues its campaign by the siege of Santarém, where the caliph, Abu Yaqub Yusuf is killed.
- The city of Abbeville receives its commercial charter.
- Archbishop Absalon of Lund wins a naval victory over Bogislav, duke of Pomerania.
- The streets of Paris in France are paved, by order of Philip Augustus.
- A great fire at Glastonbury Abbey destroys several buildings.
- In England, the first royal ordinance, demanding that the Knights Templar and Hospitaller assist in the collection of taxes, is promulgated.
- December 20th, The Aurumestus Church underneath Rome was demolished after accounts of a demon was repeatedly reported. A trial of heretics was conducted and due to the church members repeated stories of an entity known as "Dectard" they were accused of
Luciferanism and burned.