WASHINGTON—Thousands gathered Monday to watch the demolition of Sen. Robert C. Byrd, 91, who was torn down after nearly five decades as a prominent Beltway fixture. At 2:30 p.m., the once-modern senator was strategically detonated with explosive charges, causing him to collapse in a cascading succession that drew loud cheers from those in attendance. "Sen. Byrd has been a beloved Washington institution for as long as most people in this city can remember," House Speaker Nancy Pelosi said of the longest-serving senator in U.S. history, who was marked for implosion due to his leaky, dilapidated exterior and his failure to meet congressional health and safety standards. "But alas, the time has come to make way for a new generation of leadership." Sources reported that commemorative pieces of the legislator will be available for sale in the Capitol gift shop.