The Via Francigena (the Iter Francorum, or the "Frankish Route") is a branch of the Pilgrimage trail that goes between Canterbury and Rome, coming into full use starting around the 11th century.
Bishop Sigeric of Canterbury first made the journey to Rome in 990 AD to receive honors from the Pope. He kept details of his travels in a book, with pictures and maps of the route, which became the pilgrimage route of today, more or less.
The route contains lots of interesting cities, from the Roman stronghold of Aosta, with some great ruins to visit, to Ivrea, known for its orange-throwing carnevale, Vercelli for its rice (and the frogs who have a symbiotic relationship with it), Luni, for which the Lunigiana gets its name (there are over 160 castle and castle ruins to visit) and other compelling destinations like San Gimigiano and its towers and Siena with its Palio. It's a great route to trek today.
It's also a great route to take by car or train. The sudden influx of travelers in groups made travel, and subsequently trade, safer along these routes. Thus, the richest and most diverse cities with compelling 11th and 12th century architecture exist along the route.
If you'd like to walk the Italian sections of the Via, see below for the Lightfoot guides, which offer a wealth of information on trails and lodging long the route.
Some of the destinations on the Via Francigena trail of Northern Italy have information you can find by clicking or tapping on most of the town names on the map.
Via Francigena - Associazione Europea: Mostly in Italian, but you can download maps of the stages of the walk.
Confraternity of Pilgrims to Rome: Practical help and information for those making a pilgrimage to Rome by foot, bicycle or horse.
The Via Francigena - A site in English about the Via.
Le Vie Francigene del Sud - Maps and resources for the Via Francigena south of Rome to Brindisi and other east coast ports.
The first three books are essential guides to walking the Via Francigena. The last on is about the experience: find out what it's like when food lovers hit the Via Francigena. Read our review of An Italian Odyssey.