Community members, survivors and victims' families came together at Clement Park in Littleton, Colorado, to mark 20 years since the Columbine High School shooting massacre.

Details: A series of events honored those affected by the shooting, which killed 12 students and 1 teacher on April 20, 1999, including a remembrance ceremony. At the event, audience members cried and cheered survivor Sean Graves' onto the stage, the Denver Post reports. Here are some of the most powerful moments from the events.

Today marks the 20th anniversary of the attack on Columbine High School: On April 20, 1999, 2 teenage boys dressed in black trench coats killed 12 classmates and a teacher, and wounded 2 dozen others before taking their own lives.

Why it matters: Now, the survivors are raising kids in a world shaped by the attack. "Drills teaching students to 'lock down' inside classrooms became routine. Schools formed teams to assess threats, particularly from students. And security firms forged a multibillion-dollar industry, introducing surveillance video, panic buttons and upgraded doors and locks," AP reports. And, sadly, mass shootings have become part of growing up in America.