(Chris Schneider ~ Associated Press)
Flags flew at half-staff over the school and dozens of mourners lay roses and carnations at a memorial.
About 70 people gathered outside the state Capitol to push for gun control, while lawmakers inside passed a resolution honoring the victims.
"Columbine will not become just a metaphor for tragedy," Rep. Ken Summers told lawmakers before they passed a resolution called "Triumph Over Tragedy." Ten years ago, Summers was a pastor in the Columbine neighborhood.
Two seniors at Columbine unleashed an attack with guns and pipe bombs on the morning of April 20, 1999. The gunmen, Eric Harris, 18, and Dylan Klebold, 17, committed suicide.
At the gun control rally, 13 people with ribbons in school colors of white and blue wrapped around their necks lay on the ground to represent the victims and 23 others representing the wounded encircled them.
Andrew Goddard of Richmond, Va., whose son Colin was wounded at the Virginia Tech University massacre two years ago, also attended the rally. He said new police tactics that emerged after Columbine probably saved his son's life.
"They paid a huge price for that small lesson, but that lesson did benefit the students at Virginia Tech," he said.
At Columbine, police and deputies followed a standard tactic of forming a perimeter before advancing carefully toward a gunman. Afterward, many agencies adopted a policy of aggressively attacking the shooter.
Virginia Tech student Seung Hui-Cho killed 32 people and committed suicide on April 16, 2007.
A memorial service was planned for Monday night in Clement Park, next to the school in the south Denver suburbs.
On the anniversary, Oprah Winfrey canceled an episode schedule to air Monday, "10 Years Later: The Truth about Columbine."
Winfrey posted a message Monday morning on her Facebook page, saying that after she reviewed the taped show, she decided to pull it because of its focus on the two gunmen. She urged viewers to keep the Columbine community in their thoughts.
Gov. Bill Ritter had planned to address the Legislature in the House chamber Monday, but his speech was canceled at the last minute because House Speaker Terrance Carroll declined to suspend the rules.
"Traditionally, the governor doesn't come on the floor unless it's the State of the State speech, and I'm not inclined to change that precedent," said Carroll. Both Carroll and Ritter are Democrats.
Associated Press Writers Alysia Patterson, Steven K. Paulson and Colleen Slevin contributed to this story.
On the Net:
Columbine Memorial: http://www.columbinememorial.org
Columbine High School: http://sc.jeffco.k12.co.us/education/sch...