It was 2001, September 11

The north tower was about 103 stories  high, and was hit with a jet plane at about 8:30 A.M.

The south tower was a little smaller, and was hit with another jet at 9:03 A.M.

Two other jets also attacked, but I know one crashed into the Pentagon. Thanks @Lizzy_F for telling me that the other went down in a valley. I never knew that till now