My wife and I did the 'Langs oude wegen' (Along Ancient Roads) tour through France. It tries to use many roads made by Romans and passes some traditional pilgrim's sites like Vezelay and Moissac. Rocamadour was quite amazing.

The Romans didn't bother with hairpins, their roads were straight. You can still see the effect of this on a map of France. It also has obvious implications for cycling. In spite of that, the tour wasn't too difficult. I can recommend it for riding from Maastricht or Aachen to Spain.