Sept. 11, 2001
People flee lower Manhattan across the Brooklyn Bridge in New York, Tuesday, Sept. 11, 2001, following a terrorist attack on the World Trade Center.
Lead hijacker Mohammed Atta telephoned plotter Ramzi Binalshibh on Aug. 29, 2001 with a riddle to solve: "Two sticks, a dash and a cake with a stick down -- what is it?" Binalshibh decoded the message to mean that the two sticks represented the number "11" and the cake with a stick down as the number "9." It is not uncommon to write a date in which the day precedes the month -- 11-9, or the 11th of September.