People gathered Saturday at the three sites where terrorists killed nearly 3,000 people on Sept. 11, 2001, with leaders, survivors, and more paying tribute and mourning the fallen 20 years later.

Ground zero in New York, the Pentagon in Virginia, and Shanksville, Pennsylvania, hosted memorials with survivors and top U.S. officials in attendance. Lectors read the names of each of the 2,977 people killed in the attacks.