According to Classical-era mythology, after the overthrow of the Titans, the new pantheon of gods and goddesses was confirmed. Among the principal Greek gods were the Olympians, residing atop Mount Olympus under the eye of Zeus. (The limitation of their number to twelve seems to have been a comparatively modern idea.) Besides the Olympians, the Greeks worshipped various gods of the countryside, the goat-god Pan, Nymphs (spirits of rivers), Naiads (who dwelled in springs), Dryads (who were spirits of the trees), Nereids (who inhabited the sea), river gods, Satyrs, and others. In addition, there were the dark powers of the underworld, such as the Erinyes (or Furies), said to pursue those guilty of crimes against blood-relatives. In order to honor the Ancient Greek pantheon, poets composed the Homeric Hymns (a group of thirty-three songs). Gregory Nagy regards "the larger Homeric Hymns as simple preludes (compared with Theogony), each of which invokes one god".