With the TGV to Marseille
Although Marseille is located very far in the south of France, traveling by train can be faster, cheaper and more comfortable than traveling by plane. This is at least true if you live near the direct TGV connection between Frankfurt and Marseille. The TGV - the French counterpart to the German ICE - runs once a day without changing trains from Frankfurt via Mannheim - Karlsruhe - Baden-Baden - Straßburg - Mulhouse Ville and a few other stops in France to Marseille-Saint-Charles and only needs 7 from Frankfurt: 52 hours (from Karlsruhe only 6:38).
If you include the waiting and check-in times at the airport and do not have to take a direct flight but a connection, a flight to Marseille may be more time-consuming than a train journey. And such a train journey is always more ecological than flying. In addition, there are very often savings prices at Deutsche Bahn, especially for other European countries.