|Ab urbe condita||1839|
|Balinese saka calendar||1007–1008|
|English Regnal year||20 Will. 1 – 21 Will. 1|
|Chinese calendar||乙丑年 (Wood Ox)|
3782 or 3722
— to —
丙寅年 (Fire Tiger)
3783 or 3723
|- Vikram Samvat||1142–1143|
|- Shaka Samvat||1007–1008|
|- Kali Yuga||4186–4187|
|Japanese calendar||Ōtoku 3|
|Minguo calendar||826 before ROC|
|Seleucid era||1397/1398 AG|
|Thai solar calendar||1628–1629|
1212 or 831 or 59
— to —
1213 or 832 or 60
|Wikimedia Commons has media related to 1086.|
- October 23 – Battle of Sagrajas: Spanish forces under King Alfonso VI (the Brave) of Castile are defeated by the Moors and their allies, the Almoravids, who had been invited to help on orders by Emir Abbad III.
- Norman forces under Count Roger I (Bosso) conquer Syracuse, the last Muslim stronghold in Sicily.
- August 1 – King William I (the Conqueror) calls for a meeting at Old Sarum, where he invites his major vassals and tenants-in-chief to swear allegiance to him. The oath is known as the Oath of Salisbury.
- The Domesday Book is completed, which is drawn up on the orders of William I. It describes in detail the landholdings and resources in England.
- The population in England is estimated to be 1.25 million citizens with 10% living in boroughs.
- Summer – Suleiman ibn Qutulmish, ruler of the Rum Sultanate, is killed by Emir Tutush I near Antioch. Suleiman's 7-year-old son Kilij Arslan is captured and transferred as hostage to Isfahan (modern Iran).
- Sultan Malik-Shah I rebuilds the Imam Ali Mosque in Najaf (modern Iraq), after it was destroyed by fire.
- April 24 – Ramiro II (the Monk), king of Aragon (d. 1157)
- August 11 – Henry V, Holy Roman Emperor (d. 1125)
- August 20 – Bolesław III, duke of Poland (d. 1138)
- Al-Shahrastani, Persian scholar and historian (d. 1153)
- Þorlákur Runólfsson, Icelandic bishop (d. 1133)
- Vicelinus, bishop of Oldenburg in Holstein (d. 1154)
- Zhang Jun, Chinese general and official (d. 1154)
- March 15 – Richilde, countess and regent of Flanders
- March 18 – Anselm of Lucca, Italian bishop (b. 1036)
- May 21 – Wang Anshi, Chinese chancellor (b. 1021)
- July 10 – Canute IV (the Holy), king of Denmark
- July 14 – Toirdelbach Ua Briain, Irish king (b. 1009)
- July 17 – García Ramírez, Aragonese bishop
- August 8 – Conrad I, count of Luxembourg (b. 1040)
- September 25 – William VIII, duke of Aquitaine
- October 11 – Sima Guang, Chinese politician (b. 1019)
- October 23 – Rodrigo Muñoz, Galician nobleman
- December 25 – Judith of Bohemia, duchess of Poland
- Gregory Pakourianos, Byzantine politician and general
- Hui Zong, Chinese emperor (Western Xia) (b. 1060)
- Mael Ísu Ua Brolcháin, Irish monk and writer
- Muhammad ibn Ammar, Moorish poet (b. 1031)
- Odo I (or Eudes), French nobleman (b. 1040)
- Suleiman ibn Qutulmish, ruler of the Rum Sultanate