sentences:  The first farmers appeared in the Neolithic, or New Stone Age, shortly after 4000 BC.These were the first to erect megalithic monuments and evidence of their culture survives in the burial cairns, passage tombs, portal tombs and wedge tombs that can still be seen in the Dublin Mountains and on the coastal lowlands just to the south of the modern city.Stone axes made of porcellanite from County Antrim or porphyry from Lambay Island have also been discovered at a number of sites in the Dublin region.