The island came under Carthaginian dominance around 510 BC, after that a first attempt at conquest in 540 BC that ended in failure. They expanded their influence to the western and southern coast from Bosa to Caralis, consolidating the existing Phoenician settlements, administered by plenipotentiaries called "Suffetes", and founding new ones such as Olbia, Cornus and Neapolis; Tharros was probably the main centre. Carthage encouraged the cultivation of grain and cereals and prohibited fruit trees. Tharros, Nora, Bithia, Monte Sirai etc. are now important archaeological sites where Punic architecture and city planning can be studied.