In a large bowl, cover the dried beans with 2 inches of water and let them soak overnight. Drain and rinse the beans, then transfer them to a medium enameled cast-iron casserole. Add 3 quarts of the water and bring to a simmer over moderate heat, skimming as necessary to remove the foam that rises to the surface. Cook the beans over low heat until almost tender, about 1 hour. Add the tomatoes, garlic, celery leaves, oregano and 1/4 cup of the olive oil. Season with salt. Continue cooking until the beans are very tender, about 1 1/2 hours longer.