Just to the north of Arles, Provence’s chief Roman metropolis, the river Rhône divides into two : to the west the "petit Rhône" flows down to the "petite Camargue", Aigues Mortes, and les Saintes-Maries-de-la-Mer, and to the east the "grand Rhône" which embraces the salt works (Salin de Giraud) and the petro-chemical industrial complexes of Port St.Louis, Port de Bouc, and Fos sur Mer. Between and around them lies the vast delta of salt marsh known as the Camargue. Created by the ebb flow and collision of the great river from the north, swollen by melting Alpine snows, and from the southeast buffeted by a robust riposte of the "houle" (sea swell) which douses the salt flats, forever re-designing intricate patterns of pools, ponds, and lagoons "étangs", among sandbars and desolate marshland.