Shared experiences define what it means to be an American. The Sept. 11, 2001, terrorist attacks were such a unifying event for modern Americans. Nothing else has come close to being as important or as memorable, according to a new survey conducted by Pew Research Center in association with A+E Networks’ HISTORY.

The Pew Research’s Center’s use policy applies. For more, see: https://legacy.pewresearch.org/about/use-policy/