Genius loci (plural: Genii locorum) are the spirits of place. They are nature spirits that exist within the mortal world. Ancient humans often worshipped the genii locorum as gods, as evidenced most prominently by the ancient Romans. A genius loci manifests as a natural element or system of the world, i.e. forests, rivers, mountains. It is unclear why one system will create or birth a genius loci and why one won't - the spirits themselves do not know this. The four class of genius loci are Dryad, Naiad, Sylph, and Oread.