Xenia (Greek: , xenía, trans. "guest-friendship") is the ancient Greek concept of hospitality, the generosity and courtesy shown to those who are far from home and/or associates of the person bestowing guest-friendship. The rituals of hospitality created and expressed a reciprocal relationship between guest and host expressed in both material benefits (such as the giving of gifts to each party) as well as non-material ones (such as protection, shelter, favors, or certain normative rights).
The Greek god Zeus is sometimes called Zeus Xenios in his role as a protector of guests. He thus embodied the religious obligation to be hospitable to travelers. Theoxeny or theoxenia is a theme in Greek mythology in which human beings demonstrate their virtue or piety by extending hospitality to a humble stranger (xenos), who turns out to be a disguised deity (theos) with the capacity to bestow rewards. These stories caution mortals that any guest should be treated as if potentially a disguised divinity and help establish the idea of xenia as a fundamental Greek custom. The term theoxenia also covered entertaining among the gods themselves, a popular subject in classical art, which was revived at the Renaissance in works depicting a Feast of the Gods.
Xenia consists of two basic rules:
Xenia was considered to be particularly important in ancient times when people thought gods mingled among them. If one had poorly played host to a stranger, there was the risk of incurring the wrath of a god disguised as the stranger. It is thought that the Greek practice of theoxenia may have been the antecedent of the Roman rite of Lectisternium, or the draping of couches.
While this particular origin of the practices of guest-friendship are centralized around the divine, however, it would become common practice among the Greeks to incorporate xenia into their customs and manners for very much all of ancient Greek history. Indeed, while originating from mythical traditions, xenia would very much become a standard practice throughout much (if not, all) of Greece as customarily proper in the affair of men interacting with men as well as men interacting with the Gods.
The Trojan war described in the Iliad of Homer actually resulted from a violation of xenia. Paris, from the house of Priam of Troy, was a guest of Menelaus, king of Mycenaean Sparta, but seriously transgressed the bounds of xenia by abducting his host's wife, Helen. Therefore, the Achaeans were required by duty to Zeus to avenge this transgression, which, as a violation of xenia, was an insult to Zeus' authority.