Clint Seidl, whose mother died in the bombing, helps Vice President Gore turn the soil for the memorial

OKLAHOMA CITY (CNN) -- On the site where the twisted and toppled remains of the Alfred P. Murrah Federal Building once stood, friends and family of those who perished in the 1995 Oklahoma City bombing gathered Sunday to break ground on a memorial to the victims.

"The people who died here were victims of one of the cruelest visitations of evil this nation has ever seen," said Vice President Al Gore. "But we offer them today not pity but honor, for as much as any soldier who ever fought in any war, they paid the price for our freedom."

On April 19, 1995, a massive explosion caused by a truck bomb ripped through the Murrah building, killing 168 people and injuring more than 500. The bombing stands as the worst terrorist attack ever on U.S. soil.

Hundreds of people gather to mark a new beginning in Oklahoma City

The mastermind of the bombing, Timothy McVeigh, has been sentenced to death for his role in the blast; his co-conspirator, Terry Nichols, received a sentence of life without parole.

"We will not back down in the face of terrorism," said Attorney General Janet Reno, who joined Gore and a crowd of several hundred at the memorial's groundbreaking. "We'll carry on and do our duty to the country and the people, and we will not be intimidated by terrorism."

After speeches were complete, Gore took a shiny shovel and dug it into the ground. He then handed the shoved to Clint Seidl, who was in the second grade when his mother, a Secret Service agent, was killed in the bombing.

One after another, people grasped the shovel, and, dressed in their Sunday best, took turns tossing a chunk of soil into a pile.

168 glass and metal chairs will be part of the memorial

"This turning over the ground for me is a symbolic gesture of being able to raise something back on that ground of glory and beauty," said Dan McKinney, who lost his wife, Linda, in the blast.

The $24.1 million memorial will include a reflecting pool, an interactive museum and 168 glass and metal chairs, one for each of the victims. A portion of the chain-link fence that surrounds the bomb site -- which has become a shrine where visitors leave mementos -- will remain.

The fence holds "the real story of our democracy. This is how we feel," said Gore.

Correspondent Jim Hill contributed to this report.