This "lecture" is an experiment. It uses Google Earth to show one route from Paris to Milan. Along the way are short entries that talk about travel conditions, aspects of trade, and some of the towns.
You must use Google Earth for this. If you don't have it, you will have to download it (it runs on all platforms).
Once you have Google Earth, click on the link below to begin. Once you do, you'll see "Merchant Journey" in the Places panel. Work your way from there. I've included instructions there as well, but if you have questions, please ask. This is very much a beta and I welcome feedback.