Greek and in Roman mythology is a young female deity typically identified with natural features such as mountains (oreads), trees and flowers (dryads and meliae), springs, rivers and lakes (naiads) or the sea (nereids), or as part of the divine retinue of a comparable god such as Apollo, Dionysos or Pan, or goddesses, such as Artemis, who was known as the tutelary deity of all nymphs. Such is the importance of nymphs to the sacred landscape of the Greeks that when in the Iliad Zeus summons the gods into assembly on Mount Olympus, it is not only the well known Olympians in attendance, but also all the nymphs and river gods.