Traveling in Ancient Rome

The Stanford University history and IT departments have banded together to create Orbis which lets you see how quick (or slow) travel occurred during the Romand Empire. You can select the year, month (since winter would be different than summer) and then see what obstacles (mountains, for example) were in the way and the cost for getting from one place to another.  This would let the students see how long, for example it took the Germanic tribes to invade. You need only watch part of the video above to understand how to use the tool.  I found the tool on OpenCulture.