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Year 1070 (MLXX) was a common year starting on Friday (link will display the full calendar) of the Julian calendar.
- Winter of 1069–1070 – Harrying of the North: William I of England quells rebellions in the north of England, following an invasion by Sweyn II of Denmark. Widespread famine follows the devastation wrought.
- Spring – King Sweyn II of Denmark joins English rebels, led by Hereward the Wake, and captures the Isle of Ely, in The Fens of eastern England.
- April 11 – Archbishop of Canterbury Stigand is deposed.
- June 1 – Hereward plunders Peterborough Abbey, in eastern England.
- June – Denmark signs a treaty with England; Sweyn and his forces leave the country.
- August 15 – The Pavian-born Benedictine Lanfranc is appointed as the new Archbishop of Canterbury in England.
- An invasion of England by Malcolm III of Scotland is repelled.
- Hugh d'Avranches, 1st Earl of Chester, the first Marcher Lord, invades Wales, capturing parts of Gwynedd.
- A successful Byzantine counter-attack drives the Seljuq Turks across the Euphrates.
- Bergen is founded by King Olaf III of Norway; it will function as the main city and capital of Norway, until it is replaced by Oslo in 1314.
- Chinese Chancellor Wang Anshi starts the Xining Reforms (which last until 1085).
- Jews from Rouen in Normandy settle in England, at the invitation of King William I.
- The Temple of Literature, Hanoi, is established in the capital of Vietnam.
- Uyghur poet Yusuf Khass Hajib of Balasagun, in the Kara-Khanid Khanate, completes the Kutadgu Bilig ("The Wisdom Which Brings Good Fortune"), and presents it to the prince of Kashgar.
- Song dynasty Chinese astronomer, engineer, and statesman Su Song completes the compilation of the Ben Cao Tu Jing, a pharmaceutical treatise with related subjects of botany, zoology, mineralogy, and metallurgy.
- Canterbury Cathedral in England is rebuilt, following a fire.
- The rebuilding of York Minster in England begins.
- Construction of Richmond Castle in North Yorkshire, England, by Alan Rufus begins.
- Approximate date – Halsten Stenkilsson is deposed as king of Sweden, with Håkan the Red becoming king in Götaland, and Anund Gårdske being chosen as king of Svealand.