The square containing the old customs post, the Rue des Marchands and the Rue Mercière form the heart of the old town. The old Alsace dwellings are in abundance there, most picturesque with their flower-covered balconies, corbelled turrets, oriel windows and half-timbering. See especially the Pfister houses and the old customs post (or Koifhus). Also of note are the collegial Church of St Martin and the Dominican Church for its celebrated painting of Virgin in the rose bush.