Heat olive oil in a large enameled casserole. Add onions, carrots, celery and garlic. Cover and simmer, stirring on occasion, for 10 minutes or until really tender. Add the white wine and reduce by half. Add the tomatoes and their juices and simmer for 20 minutes to mellow the flavor. Add the mussels, cover the casserole and cook over high heat until they open. Discard unopened mussels. Spoon mussels and their liquid in deep bowls and garnish with basil. Could also serve over pasta or rice or with a potato salad.