Year 1115 (MCXV) was a common year starting on Friday (link will display the full calendar) of the Julian calendar.
September 14 – Battle of Sarmin: The Crusaders, under Prince Roger of Salerno, surprise and rout the Seljuk Turkish army (some 8,000 men), led by Emir Bursuq ibn Bursuq, at Sarmin (modern Syria). Bursuq barely avoids capture, and escapes with a few hundred horsemen. Roger reoccupies the fortress of Kafartab, and consolidates his territory around Antioch.
The Crusader castle of Montreal (located in Jordan) is commissioned by King Baldwin I of Jerusalem, during an expedition against the Seljuk Turks.
February 11 – Battle of Welfesholz: Duke Lothair of Supplinburg joins the rebellious Saxon forces, and defeats the German Imperial Army of Emperor Henry V at Welfesholz, in Saxony-Anhalt (modern Germany).
July 24 – Matilda, margravine of Tuscany, dies at Bondeno. During her reign she waged an intermittent war with Emperor Henry IV over the inheritance rights of her fiefs in Lombardy and Tuscany.
The Jin Dynasty (or Great Jin) is created by the Jurchen tribal chieftain Taizu (or Aguda). He establishes a dual-administration system: a Chinese-style bureaucracy to rule over northern and northeast China.
The 19-year-old Minamoto no Tameyoshi, Japanese nobleman and samurai, gains recognition by suppressing a riot against Emperor Toba at a monastery near Kyoto (approximate date).
The Mixtec ruler Eight Deer Jaguar Claw (or 8 Deer) is defeated in battle and sacrificed by a coalition of city-states, led by his brother-in law 4 Wind, at Tilantongo in the Mixteca Alta region (modern Mexico).
Arnulf of Chocques is accused of sexual relations with a Muslim woman. He is briefly removed from his position as patriarch of Jerusalem.
Peter Abelard, French scholastic philosopher, becomes master of the cathedral school of Notre-Dame and meets Héloïse d'Argenteuil.
Clairvaux Abbey is founded by Bernard, French abbot and a major leader in the reform of Benedictine monasticism, in France.
Hugh of Saint Victor, French theologian and writer, joins the Victorines (at the Augustinian Abbey of St. Victor) in Paris.
April 18 – Gertrude, German duchess and regent (d. 1143)
September 18 – Wu, Chinese empress consort (d. 1197)
Aubrey de Vere, 1st Earl of Oxford (approximate date)