1999 (real world)

1999 is the year Halo was first announced.

February
February 15
 * The first Cortana letter was released.

March
March 16 March 18
 * The second Cortana letter was released.
 * The third Cortana letter was released.

May
May 10
 * The fourth and fifth Cortana letters were released.

June
June 30
 * The sixth Cortana letter was released.

July
July 7 July 21
 * The seventh Cortana letter was released.
 * Halo is unveiled at the Macworld Expo in New York.

September
September 13
 * The eighth Cortana letter was found.

November
November
 * One of the first screenshots of Halo was released in Computer Gaming World Magazine.