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|Ab urbe condita||1837|
|Balinese saka calendar||1005–1006|
|English Regnal year||18 Will. 1 – 19 Will. 1|
|Chinese calendar||癸亥年 (Water Pig)|
3780 or 3720
— to —
甲子年 (Wood Rat)
3781 or 3721
|- Vikram Samvat||1140–1141|
|- Shaka Samvat||1005–1006|
|- Kali Yuga||4184–4185|
|Japanese calendar||Eihō 4 / Ōtoku 1|
|Minguo calendar||828 before ROC|
|Seleucid era||1395/1396 AG|
|Thai solar calendar||1626–1627|
1210 or 829 or 57
— to —
1211 or 830 or 58
|Wikimedia Commons has media related to 1084.|
- March 31 – Emperor Henry IV besieges Rome and enters the city. He is crowned emperor by Antipope Clement III at Rome and receives the patrician authority.
- May – Sack of Rome: Duke Robert Guiscard leads a Norman army (36,000 men) north and enters Rome, the city is sacked and Henry IV is forced to retreat.
- Robert Guiscard returns with 150 warships in Illyria (modern Albania), and occupies Corfu and Kefalonia with the support of Ragusa and the Dalmatian cities.
- King Halsten Stenkilsson is killed and his brother Inge the Elder is deposed in Svealand (modern Sweden). Inge is replaced by his brother-in-law Blot-Sweyn.
- The Seljuk Turks under Sultan Malik-Shah I conquer Byzantine Antioch, held by Philaretos Brachamios, an Armenian general, who seize power as a usurper.
- Sima Guang, Chinese chancellor and historian, completes with a group of scholars the Zizhi Tongjian, a chronicle of the universal history of China.
- April 21 – King Kyansittha begins his reign as ruler of the Pagan Kingdom in Burma (modern Myanmar).
- Pope Gregory VII, who is imprisoned by Henry IV in Castel Sant'Angelo, is freed by Robert Guiscard. He restores papal authority in Rome.
- Bruno of Cologne founds the Carthusian Order which includes both monks and nuns. He builds an hermitage in the French Alps.
- Building work starts on Worcester Cathedral. Orchestrated by Bishop Wulfstan.
- August 1 – Heonjong, Korean king of Goryeo (d. 1097)
- Alan I (le Noir), viscount of Rohan (d. 1147)
- Ali ibn Yusuf, ruler of the Almoravids (d. 1143)
- Bahram-Shah, ruler of the Ghaznavids (d. 1157)
- Charles I (the Good), count of Flanders (d. 1127)
- David I, king of Scotland (approximate date)
- Li Qingzhao, Chinese female poet and writer
- Rainier, margrave of Montferrat (approximate date)
- Rechungpa, Tibetan founder of the Kagyu school (d. 1161)
- Wang, Chinese empress of the Song Dynasty (d. 1108)
- February 16 – Siegfried I, archbishop of Mainz
- June 28 – Ekkehard of Huysburg, German abbot
- October 10 – Gilla Pátraic, bishop of Dublin
- November 20 – Otto II, margrave of Montferrat
- Aghsartan I, Georgian king of Kakheti and Hereti
- Fujiwara no Kenshi, Japanese empress (b. 1057)
- Halsten Stenkilsson, king of Sweden (approximate date)
- Herfast (or Arfast), Norman Lord Chancellor
- Hoël II, duke of Brittany (House of Cornouaille)
- Saw Lu, king of the Pagan Kingdom (b. 1049)