1999 (real world)

In 1999, is the year Halo was first announced.

February

 * February 15: The first cortana letter was released.

March

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

May

 * May 10: The fourth and fifth Cortana letter was released.

June

 * June 30: The sixth Cortana letter was released.

July

 * July 7: The seventh Cortana letter was released.
 * July 21: 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.