Like its neighbour Savu, Roti is dry and not very fertile. Historically, the islanders subsisted primarily upon the sap of the lontar palm, which grows abundantly on the island. The indigenous Rotinese religion involved two classes of spirits: spirits of the inside (benevolent ancestral spirits), and spirits of the outside (malevolent spirits of unknown origin). While Christianity has been practiced on Roti for centuries, most of the population did not convert until well into the twentieth century.