The First Crusade takes Jerusalem after a siege, followed by a massacre of its inhabitants.
Date given in the Julian calendar.
The Seljuks defeat and capture Byzantine Emperor Romanos IV, opening Anatolia to Turkish settlement.
Papal legates lay a bull of excommunication on the altar of Hagia Sophia, marking the split between Roman Catholic and Eastern Orthodox churches.
Launched after the fall of Edessa and led by Louis VII of France and Conrad III of Germany, the crusade ends in failure before Damascus.
Ibn Sina (Avicenna) completes The Canon of Medicine, a medical encyclopedia used as a standard text in the Islamic world and Europe for centuries.
Ibn al-Haytham composes the Book of Optics, explaining vision as light entering the eye and emphasising experimental method.
Saladin destroys the army of the Crusader Kingdom of Jerusalem near Tiberias, causing most Crusader strongholds to fall.