Even before the U.S. Park Police estimated Monday's crowd at 400,000, authorities knew the figure would be controversial. It always is.
As has happened with many previous demonstrations, those who plan and carry out such events "usually see the turnout more with their hearts than their eyes," as one government official put it. For that reason, Park Police figures are a sensitive measure.
Setting the stage for controversy, Benjamin F. Chavis Jr., co-organizer of the "Million Man March," said even before the program began that the crowd exceeded 1 million. At the time, however, large areas of the Mall were only sparsely filled.
Park Police, aware that critics often accuse them of making conservative crowd estimates, claim they have had more than 30 years' experience in judging massive Washington turnouts and that their methods are scientific.
A central feature of their technique is the use of a grid system and aerial photographs to gauge the size of turnouts on the Mall. They count the number of people in individual sections of the grid, then multiply them to arrive at the overall figure.
The largest capital demonstration was said to be the November, 1969, Vietnam War moratorium rally, which officially drew 600,000 protesters, many of whom encircled the Pentagon. Three political events drew an estimated 500,000 marchers: the 1971 Vietnam War "Out Now" protest, the 1981 welcome home for Americans held in Iran and a 1992 abortion rights march.