Do You Know this Plant?

There are times when the harsh growing conditions of beautiful flowers astound me.

This beautiful, cascading plant was literally growing out of a stone wall in Gourdon, France. I took this photo on May 7th this year, so I assume that this blue-purple flower must be a spring-blooming plant. The wall is in a central plaza in Gourdon, in full sun, south-facing.

Is it a self-seeding annual or a perennial? The blossoms remind me of a type of campanula, but I'm not familiar with this cascading form.

This is a garden inspiration since I have a lot of stone in the garden. I have successfully planted sedum and creeping jenny in the bare rock along the stream, but I'd love to try something that blooms profusely like this cascading flower in France.

Update from a reader: These are Edraianthus, though I am not certain of the exact variety (there are about 8 varieties that I know of). Edraianthus are members of the campanula family, hence why everyone thought they were bellflowers. Check out this link for a photo:
Edraianthus