A. Here is an essential fact about ancient Greek religion (for a working definition of this general term, see item B): not only were the gods worshipped. Heroes too were worshipped. The worship of heroes was very much like ancestor worship. (Compare similar customs in other traditional societies, including the Japanese.)
A1. Besides the word worship, we may use the word cult. As in the expression hero cult. Other relevant concepts: cultivate [as in "cultivating" a field / garden / grove / orchard / vineyard / etc.] and culture [as in the opposition of "cultural" vs. "natural," that is, "artificial" vs. "natural"].
A2. It is a historical fact that the ancient Greeks worshipped heroes throughout the period covered by the texts that we read in the "Heroes" course, starting already with the Homeric Iliad and Odyssey (the oral traditions that culminated in these epics were beginning to crystallize around the eighth century BCE) and ending with the Heroikos of Philostratus (around 200 CE).
A3. Even if we had no epic (Homeric Iliad and Odyssey) or drama (tragedies of Aeschylus, Sophocles, and Euripides) surviving from the ancient Greek world, we would still be fairly well informed, on the basis of non-poetic evidence (prosaic references, inscriptions, archaeological remains of cult sites, etc.) about the historical existence of hero cults in the period extending from (roughly) the eighth century BCE through the third century CE and even beyond.
A4. The 1979 book The Best of the Achaeans (new ed. 1999) was the first book in Classical scholarship to argue, as a central thesis, that the non-poetic evidence about the religious practice of hero-cults can be systematically connected with the existing poetry and with what that poetry says - directly or indirectly - about this religious practice. The book was meant to demonstrate that such non-poetic evidence enhances our appreciation of the poetry, especially the epic traditions of Homer (and the dramatic traditions of Aeschylus, Sophocles, and Euripides). Another central thesis of the book was that the poetry itself provides additional new evidence about the practice of hero cults.
B. For a working definition of ancient Greek "religion," I suggest simply: the interaction of ritual and myth. A working definition of ritual and myth:
B1. Ritual. In small-scale societies, what you do in sacred space is marked activity, any kind of marked activity, most obviously worship (cult) and sacrifice, but also including: hunting, athletics, regulated sexual relations, even warfare.B1a. Specially difficult for us to understand: sacrifice (killing animals, cooking by fire, and distribution in community) and warfare. Sacrifice is a ritualized admission of human guilt about the human capacity to kill other humans, as in warfare. This formulation was developed by Walter Burkert in a book about the anthropological background of sacrifice: Homo necans (as opposed to Homo sapiens).
B1b. Working definition of "sacred space": whatever is set aside by society for communication with the world beyond our everyday world. It is marked space vs. unmarked space. "Sacred" is the best way to describe "marked" in the smallest-scale societies. I try to stay away from words like divine, even supernatural.
B2. Myth. In small-scale societies, what you say in sacred space is marked speech, any kind of marked speech, most obviously worship (cult) and prayer, but also including: oaths, wagers, promises; these are typical speech-acts. In ancient Greece, there were other kinds of speech-acts that we ordinarily would not think of as speech-acts: laments, insults, praise, instruction; in other words, anything formal that is on record, as it were; to say on the record as opposed to off the record; marked vs. unmarked; marked speech is automatically witnessed by the gods or whatever is out there beyond the everyday world, in the sacred world. Myth explains the way things are. In some song cultures, it has maximum truth-value.B2a. An illustration of the power of the speech-act... "The phrase is a holy being. You see, these songs, when they were turned over to the Earth People, were to be used in a certain way. If you leave out those words, then the holy beings feel slighted. They know you are singing, they are aware of it. But if you omit those words, then they feel it and they are displeased. Then, even though you are singing, whatever you are doing ... has no effect." - from an interview with a Navajo shaman.
B3. One of the most fundamental facts about ancient Greek religion is that it tends to be local and localized. For myth to be delocalized, as it tends to be in Homeric poetry (also in most archaic and classical poetry), it has to be separated from ritual.
B4. Everything that you have read so far about ritual and myth involves heroes as well as gods in ancient Greek religion.
C. Fifteen basic facts about hero cults.
#1. Hero cult was a fundamentally local practice, confined to a specific locale. There were literally thousands of hero-cults throughout the locales of the ancient Greek-speaking world. Every locale had its own set of local heroes. (For example, in the "demes" or local districts that constitute the urban / rural complex of Athens, each "deme" has a variety of local cult heroes.) Some of these heroes are well known to us through epic (every hero - major or minor - mentioned in the Iliad and Odyssey was potentially a local hero) and tragedy, while others are never mentioned in any poetry known to us. The local hero of hero cult could be male or female, adult or child.
#2. Ordinarily, the hero cult was based on the presence of the sôma 'body' (corpse) of the hero in the "mother earth" of the given locale. (Occasionally, the presence was limited to only a part of the body - like the head.) Whatever we may think scientifically about the identity of the given corpse in any given case, the locals understood that body (or body-part) to belong to the hero. The practice of venerating bodies or body-parts (or, metonymically, various objects associated with the bodies) continued beyond ancient Greece; an aspect of continuity is the Christian practice of venerating the relics of saints.
#3. The sôma of the dead hero was considered to be a talisman of fertility and prosperity to the community that worshipped the hero. The fertility was viewed in terms of plant life (especially the harvests from the fields, gardens, groves, orchards, vineyards, and so on), animal life (both domesticated and hunted animals), and human life (literally, sexuality and the producing / nurturing of children).
#4. The "marker" of the sôma was the sêma, which ordinarily took the physical shape of a 'tomb'.
#5. The "marking" of the sôma could also be a sign or signal or token or picture; the word for such a "marking" was also sêma.
#6. The "marking" would be a sacred secret in some situations. The local details of ritual and myth surrounding a given hero cult were held to be sacred in any case; as such, they tended to be considered secret as well. Or, at least, some of the sacred details were screened by the locals as secrets that must not be divulged to outsiders. The "outsiders" were not only the non-locals: they were also those of the locals who had not yet been initiated - the word for which is muô - into the secrets - the word for which is mustêria 'mysteries'. In Latin, the word for 'uninitiated' is profanus 'profane' (= 'standing in front of [= not inside] the sacred space').
#7. When locals sacrificed to a hero, they would kill a sacrificial animal (victim) and then divide its meat among the participants in the sacrifice, keeping the choice cut of meat, called geras, as an offering to the hero. To give heroes their proper geras was to give them their proper timê 'honor'. For more on timê, see also below.
#8. Another aspect of sacrificing to the hero was the ritual pouring of liquids, that is, libations; besides such liquids as water, wine, oil, milk, emulsified honey, and so on, the actual blood of the sacrificial victim could also count for the pouring of certain special kinds of libations. For example, the pouring of blood into the earth in order to make physical contact with the corpse of a hero below (sometimes a tube was connected to the mouth of the corpse) was thought to activate the consciousness of the hero, so that the hero could then give advice (= give a diagnôsis) from down below concerning questions of fertility and prosperity. The hero was sometimes given the euphemistic name of 'healer' (Iatros, Iasôn = Jason, etc.).
#9. When worshippers sacrificed to a hero, the perspective was directed toward the earth (khthôn); when they sacrificed to a god, the perspective was directed toward the sky (ouranos), except for a special category of gods called "chthonic" (khthonioi), who likewise required the downward perspective. Note the Heroikos of Philostratus: at the beginning, we see how the Phoenician has his gaze fixed upward toward the sky, while the vineyard-keeper has his gaze fixed downward toward the earth under his feet.
#10. When one sacrifices to a hero or a god, the generic term is thuô. When one sacrifices to a hero, the specific term is en-agizô. When one sacrifices to a god, there is no specific term, unless the god is "chthonic" (in which case, en-agizô is the appropriate term). The word en-agizô means literally 'I take part in the pollution'. In poetry, thuô 'sacrifice' is equivalent to the process of giving timê 'honor' to a given hero or god. A classic example of timê in the context of hero cult is Homeric Hymn to Demeter 261; see Nagy, The Best of the Achaeans p. 118.
#11. The most common sacrificial animal to be killed and cooked in the cult of a male hero was a ram.
#12. In any sacrifice to a hero, the process was usually visualized as happening beneath earth-level (the sacrifice is directed toward a depression in the earth, as into a pit or bothros). In any sacrifice to a god (with the exception, again, of the chthonic gods), the sacrifice was visualized as happening above earth-level (the sacrifice is directed toward an elevation from the earth, as on an altar or bômos). A classic example is the ritual involving the sacrifice of a black ram at the Pit of Pelops during the night before the Olympics begin and the boiling of mutton at the Altar of Zeus on the next day; see Nagy, Pindar's Homer pp. 123-124 on the testimony of Philostratus, On Gymnastics 5-6.
#13. The sacred space assigned the hero in hero-cult could be coextensive with the sacred space assigned to the god who was considered the hero's divine antagonist. A classic example is the location of the body of the hero Pyrrhos in the sacred precinct of Apollo at Delphi; see Nagy, The Best of the Achaeans ch.7 ("The Death of Pyrrhos").
#14. The hero was considered dead in terms of the place where the hero's corpse was situated; at the same time, the hero was considered immortalized in terms of the paradise-like place that awaited all heroes after death. Such a paradise-like place, which was considered eschatological, must be contrasted with Hades, which was considered transitional. The name and even the visualization of this otherworldly place varied from hero cult to hero cult. Some of these names are: Elysium, the Islands of the Blessed, the White Island, and so on. Many of these names were applied also to the actual place of the hero cult. For an extended discussion, see Nagy, The Best of the Achaeans ch.10 ("Poetic Visions of Immortality for the Hero").
#15. Heroes were thought to be capable of coming back to life (anabiônai) not only eschatologically, in their timeless paradise-like abodes, but also sporadically in the present time of their worshippers. Such sporadic "live" appearances were considered to be epiphanies. At the moment of worship, the sacred precinct of the cult hero could become notionally identical to the paradise-like abode of immortalization from which he or she returns to his worshippers. Metonymically, the sacred precinct of the cult hero needed to be a place of cultivation, such as a cultivated field / garden / grove / orchard / vineyard / etc.
Source: "Relevant facts about ancient Greek hero cults," by Gregory Nagy. Used by permission.