The Lincoln Memorial -- and the rest of the Mall -- is a popular site for protests and rallies. Here are some noteworthy ones that show how hard it is to measure the size of a protesting crowd. With Glenn Beck's Saturday rally, it's best to be wary of estimates.
Al Sharpton's 'Reclaim the Dream' march Photos | The Rev. Al Sharpton and other civil rights leaders rallied in Northwest Washington and planned to march to the Mall, to the site where a memorial to Dr. Martin Luther King Jr. is being built.