Not Your Sweetie

Washington Post on the Protest

This time, they said, the turnout was 500,000. Metropolitan Police Chief Charles H.
Ramsey said he would not provide an estimate, but said it was bigger than October's.
"It's one of the biggest ones we've had, certainly in recent times," he said.

and

Regardless of the exact number, the crowd today on the Mall was the largest anti-war
demonstration here since the Vietnam era. People packed much of four long blocks of
the Mall, shoulder-to-shoulder in many sections, from 3rd to 7th streets SW between
Madison and Jefferson drives for the 11 a.m. rally. The first marchers stepped off at
about 1:30 p.m., and when many had begun reaching the Navy Yard more than two
dozen blocks away about an hour later, protesters were still leaving the rally site.
Also, SF Chronicle:

In Washington, where temperatures hovered in the mid-20s, as many as
500,000 protesters rallied outside the Capitol, while in San Francisco
tens of thousands of peace activists marched up Market Street from the
Ferry Building to City Hall.