It’s originally a 2 panel/figure page evoking a comparison between Hannibal's campaign over the Alps with vs. Napoleon's French Army in Russia 1812-1813
Sarah Rendgen just recently got a book published on the topic:
The Minard System: The Complete Statistical Graphics of Charles-Joseph Minard
Here is the whole print in question:
Landsteiner makes notes on this, with a section in a previous article too:
 https://en.wikipedia.org/wiki/File_talk:Minard.png (note that it is actually a Commons image, so there are two talk pages for the same file)
(Many years ago I went to a talk by Dennis Ritchie about *roff. He showed the graphic and said that someone at Bell Labs had taken the time to code it up. I have no idea if that person is Ms Morse, though.)
Edited for clarity since I apperently got downvoted
edit: Some other things he suggested: don't use powerpoint. Write a technical document and have everyone read it before the meeting. He also showed how he himself could have saved the space shuttle discovery.
Sorry if I'm coming off as a bit negative. I like the books, they have some good insights but the seminar itself was terrible.
The one I went to was held at Stanford and we had a lunch afterwards where questions and discussions were entertained. The questions definitely broke down into the three classes of 'fan', 'learner', and 'skeptic'. I was fairly put off by the treatment of skeptics, in that the answers or discussion they received were of the form, "hey you paid to be here, if you don't like it just leave." Which doesn't really help.
Personally I got a lot of out both the seminar and the books. I certainly approach the development of infographics in my presentations differently than I did before being exposed to his material. I try to have graphics that convey the primary point easily (for people skimming), supporting data (for people who are trying to understand the point), and other related correlations (for skeptics who want to dispute the point). It takes more time, but it gives you something much more substantive to have up on the screen while you are discussing the point in a group.
The books on the other hand pretty much define a kind of critical thinking about visualization that's very good.
It's nice to think that something you dream about is in fact something fantastic.
Tufte had a huge impact on me too, around the same timeframe (2001.)
This is very good general advice. If more people followed it it would save a lot of trouble throughout government and industry.
The caveat is that Tufte principles are rooted in a 2D print domain, so applying his ideas to interactive or 3D domains requires some discipline.
Sparklines in Google Sheets are a classic example of applying Tufte designs to the web.
At the risk of straying, I brought a journal article comparing FeLV vaccine efficacy that caused my vet to change his sourcing.
His seminars are, in my personal experience, a light introduction to his work for the high points, and him spending 20 minutes showing us his twitter timeline for the low points.
I’d recommend buying the books, and dedicating the day you’d have spent on the seminar reading them instead.