Sept. 11, 2001 is a historic day in America and around the world.
For many, it felt like the world stood still as they watched or heard about the collapse of the Twin Towers, then the crash into the Pentagon and, finally, the crash of United Airlines Flight 93.
The day has gone down in history as one of the most tragic days in the country, claiming the lives of nearly 3,000 people and injuring more than two times as many.
During past anniversaries, the hashtag #WhereWereYou surfaced on social media as many people recounted where they learned of the attacks.
Many of the heartbreaking messages convey how people felt. Dozens showed that the attacks happened when many social media users were young and detailed how their families reacted, shaping the gravity of the news.