We have connected all the way, via the Francigena, La via della Costa, the voie Aurelienne, and the route from Arles.
Unless it is of special religious importance to you, I can think of better pilgrim trails.
Here's some links:
http://www.compostelle-paca-corse.info/Chemin/chemincompostellepaca.html
http://www.camminafrancigena.it/it/
http://www.viadellacosta.it/?lang=en
I wrote this on via Della Costa:
Extending from the French Italian border, on the Mediterranean coast, to the town of Sarzana, where it joins the via Francigena, is the lesser known route of the via Della Costa. It is indeed a historical route, following the ancient Roman via Aurellian, but it was probably no more than a local collector for medieval pilgrims making their way to and from Rome. It crosses some rough terrain, and while the Romans indeed had a great road upon which they could move an army to Arles on short notice, the route quickly evaporated upon the fall of the Roman empire, the stones used for sheepherder huts and the like. The main route for St James pilgrimages was probably north of the coastal mountains. To us, it was a natural connection of the French Chemins St Jacques and the via Francigena. It would tie us from Rome to Santiago.
Recently a group of Italians have done a nice job of marking out a route and putting together a guidebook and website.
http://www.viadellacosta.it/
Guidebook: La Via Della Costa by Monica D’Atti , Franco Cinti
The route is fairly well marked, with our familiar blue and yellow shells.
This is a bit of a schizophrenic route, which is less than ideal for either the cycling or walking pilgrim. The three personalities are:
Inland Historical. The route goes inland from the coast in several areas, connecting little mountain villages, some clinging to the slopes in a manner similar to towns in the Nepalese Himalaya. Pieces of Roman road and bridges abound, and many of the towns are genuinely old, but holy crap, it is tough going. Some days we pushed our lightly loaded bikes more in a day than we did the entire
Camino Frances.
Coastal converted trail: We spent some idyllic days on the Italian Riviera, biking on dedicated pedestrian/bike routes right along the sea. These portions follow old rail beds and roads which have since been replaced by modern roads a bit inland, leaving the old road to be left to the non-motorized recreation. Some of what we rode was official via Della Costa, some was our detours escaping the tough inland route.
Busy coastal roads: These portions are the routes undoing. There are sections where the only way to connect it up is to join all the trucks and buses and cars crowded into a narrow road, often with a cliff to the north and a guardrail to the south. The Italian drivers are tolerant of bikes, totally unaccustomed to backpackers, and life becomes miserable for everyone. The forty km west of Genoa is awful. If you walk it, take a bus through there, if you bike, well, starting at five am on a Sunday might be a good idea.
Of course, east of Genoa one arrives in the magical land of the Cinque Terra, some of the most amazing walking villages in the world. We found these isolated fishing villages to be a bit hollowed out and touristy, but what scenery!
I don't mean to scare anyone of this route. If you want to connect Rome to Santiago, the via Della Costa will get you there, but It is for the experienced pilgrim. I would say it would be perfect for a walking pilgrim who wasn’t too much of a purist to take the odd bus or train.
We had no trouble finding nice places to stay (the agriturismos are wonderful), but we were not on a tight budget and we avoid church sponsored lodging. The society has put together a fairly good list of options, and if you can speak some Italian and plan ahead, cheaper lodging is out there.