Except for this Frenchman, Ernest Chaussons, who wrote a tone poem and an opera directly inspired by the Arthurian legends. Chausson was a "bridge" figure, connecting the earlier era of French romanticism with the emergent forms of Impressionism that followed the Romantics. Chausson was primarily influenced by Wagner and by Cesar Franck, and even though his output was small, his music is highly individual and deeply felt. In this way--and in his untimely death--Chausson almost seems like a French counterpart to Alexander Borodin.
The tone poem Viviane is inspired by the love affair between Merlin the wizard and the maiden Viviane, which ends tragically in the eternal imprisonment of Merlin inside a cave of crystal. The work is lush and mostly introspective, but with passages of rapturous passion before concluding on a sad note. One can definitely hear in this work the drama of a Wagner but also the atmospheric introspection of the impressionists to come.
Here is Viviane by Ernest Chausson.