My daughter and I pooped out after an hour and a half. My wife wound up marching near Jesse Jackson and Al Sharpton. No surprise about the the train outage at Amtrak. No way just a 100,000. I did my own estimate. While taking a break from marching, we sat on the side. I took a mental picture of a group of people (it numbered 30). Every time I saw a group of 30 I noted that. In two mintues I saw 30 groups of 30. 900 people in two minutes equals 27,000 people in an hour.
And this was at a point when the parade thinned out (people would sometimes stop in front of White House and yell at an imaginary President). Not everyone marched in the parade-a lot just hung out at the Washington Monument. You do the math. Here is a slide show with images from the Washington Post combined with assorted sounds from my digital recorder.