1099 (MXCIX) was a common year starting on Saturday of the Julian calendar, the 1099th year of the Common Era (CE) and Anno Domini (AD) designations, the 99th year of the 2nd millennium, the 99th year of the 11th century, and the 10th and last year of the 1090s decade. As of the start of 1099, the Gregorian calendar was 6 days ahead of the Julian calendar, which was the dominant calendar of the time.

• Siege of Jerusalem during the First Crusade:
  • July 8 – 15,000 starving Christian soldiers march around Jerusalem.
  • January 13 – Crusaders set fire to Mara, Syria.
  • July 15 – Christian soldiers under Godfrey of Bouillon, Robert II of Flanders, Raymond IV of Toulouse and Tancred take Jerusalem after a difficult siege, killing nearly every inhabitant.
• August 12– the crusaders defeat the Fatimids at the Battle of Ascalon.