Here's a nifty new tool. Harvard University has just released a beta version of the
Digital Atlas of Roman and Medieval Civilizations (DARMC). You can use it to construct customized maps of Europe and the Mediterranean world, including physical features, the political boundaries of various kingdoms and periods, Roman roads, medieval universities, fairs and markets, and other useful details.
I'm up to my ears in a chapter at the moment, but I promise there are more posts coming.