The Saint-Trophime Catholic Church holds a prominent corner of the large square in the center of Arles that once was the Roman forum. It was first constructed in the 12th century.
It was built in the Romanesque tradition as you can tell from the pillars fronting the entrance. When it comes to medieval churches, I prefer Gothic structures with their tall pointed arches, their asymmetry, their gargoyles…. Still, inside Saint-Trophime church there are some Gothic touches, and the vaulted heavy stone arches have that impregnable medieval uplift.
But I have to admit, as much as these formidable fortresses of worship take me back to my youth taking part in Christmas pageants up by the altar of Rockefeller Chapel at the University of Chicago, I more and more gain an an appreciation of the simple Quaker Meeting House. The lack of hierarchy such a place implies, unlike the priestly preserve of a cathedral, and the idea that a congregation should be able to face each other instead of being directed to look ahead and look up, well, it has a growing appeal.
Yes, the Romanesque architecture can seem heavy when compared to Gothic. But the great joy of St. Trophime is the sculpture on the west front. In general, Romanesque portal sculpture is very dramatic. They were really concerned with the saved and the damned. Hell certainly didn’t look like fun! One of the very best is the tympanum on the church of St. Foy in the little (and still picturesque) village of Conques. Not sure if it is on your proposed route, but definitely worth a detour.