The 1170s was a decade of the Julian Calendar which began on January 1, 1170, and ended on December 31, 1179.
- Saladin abolishes the Fatimid Caliphate, restoring Sunni rule in Egypt.
- Manuel I Comnenus orders all the Venetians in the Byzantine Empire to be arrested, and their property confiscated.
- Rhys ap Gruffydd agrees to negotiate with Henry II of England.
- Construction of the Cathedral of San Sabino in Bari is completed.
- Serbian ruler Stefan Nemanja begins his sole reign.
- Alfonso II of Aragon conquers Caspe and Teruel.
- Henry II of England invades Ireland with the aid of the ousted King of Leinster, Diarmait Mac Murchada (dies May 1). As is usual at this time, Henry commandeers merchant ships as part of his invasion. Henry claims the ports of Dublin, Waterford, and Wexford for himself, and promises the Irish chieftains protection if they will acknowledge him as their overlord. This begins eight centuries of conflict between Ireland and England. Ascall mac Ragnaill, last Norse–Gaelic King of Dublin, is captured while trying to retake Dublin from the Cambro-Norman Richard de Clare (Strongbow), perhaps in company with Sweyn Asleifsson, and beheaded; before the end of the year, de Clare relinquishes possession of the city to his own liege lord, Henry.
- Pisa and Florence form an alliance against Lucca and Genoa.
- The successors of Robert Burdet leave Catalonia for Majorca, marking the end of the attempts to create a Norman principality in Iberia.
- April-May – Béla returns to Hungary, where he is acclaimed king.
- Richard Lionheart becomes Duke of Aquitaine (later King Richard I of England).
- Henry II of England and Humbert III, Count of Savoy agree to wed their respective heirs, John of England and Alicia. The alliance never occurs because Henry's elder heir, Henry the Young King, becomes jealous over the castles which the elder Henry promises to the couple, and stages a rebellion which will take the elder Henry two years to put down. By that time, Alicia has died.
- Alberto di Morra is sent by Pope Alexander III to the Council of Avranches, where Henry II of England is absolved of the sin of murder, in the matter of the assassination of Thomas Becket.
- The Synod of Cashel ends the Celtic Christian system, and brings them under the Pope.
- A Muslim rebellion is quelled at Prades; this event marks the end of the pacification of the lands recently conquered by the Catalans.
- According to the annals of the Worcester Priory, "nothing memorable" happens in this year.
- January 5 – On the death of Bolesław IV the Curly, High Duke of Poland, he is succeeded by Mieszko III the Old, and as Duke of Sandomierz in Lesser Poland by Casimir II the Just.
- March – Henry the Young King of England withdraws to the French court, marking the beginning of the Revolt of 1173–74, in which Eleanor of Aquitaine and her sons rebel against her husband Henry II of England.
- William de Braose, 3rd Lord of Bramber, becomes High Sheriff of Herefordshire in England.
- Abergavenny Castle is seized by the Welsh.
- Following the death of Kol, Canute I of Sweden (Knut Eriksson) extends his rule to also include Östergötland. He is now unopposed as king of Sweden.
- The efforts of the Almohad caliph, Abu Yaqub Yusuf, to repopulate the western Andalusian city of Beja begin. They are rapidly abandoned, sign of the quick demographic weakening of the Muslims in the peninsula.
Arts and leisure
= Western Asia =
- The last Toltec king commits suicide.
- Under the admirals of the clan Banu Mardanish, an Almohad fleet suffers a large defeat at the hand of the Portuguese, as they are trying to reconquer Lisbon.
Art and science
- 23–30 August – Battle of Jacob's Ford, Syria: Saladin destroys the still-in-construction Castle of Chastellet at Jacob's Ford, killing 700 knights and taking 800 civilians captive.
- The Maya city of Chichen Itza is sacked and burned by Hunac Ceel, the Mayapan king.
- June 19 – Battle of Kalvskinnet (outside Nidaros, Norway): Earl Erling Skakke is killed, and the battle changes the tide of the civil wars.
- Afonso I is recognized as King of Portugal by Pope Alexander III, bringing Portugal the protection of the Catholic Church against the Leonese monarchy.
- November 1 – Philip II is crowned King of France. He assumes his office, however, in the next year, following the death of his father Louis VII.
- The city of Aberdeen is chartered by William the Lion.
- A large offensive, by the Almohad army in southern Portugal, aims at the reconquest of the Alentejo. Further north, a fleet led by Abd Allah b. Ishaq b. Jami is sails to attack Lisbon, but is repelled by the Portuguese admiral D. Fuas Roupinho, near the Cape Espichel. The Portuguese admiral later manages to enter in the harbor of Ceuta, and destroy a number of Muslim ships. It is the beginning of a four-year naval conflict between the Almohads and Portuguese.