The ancient Greeks worshipped many gods, each with a distinct personality and domain. Greek myths explained the origins of the gods and their individual relations with mankind. The art of Archaic and Classical Greece illustrates many mythological episodes, including an established iconography of attributes that identify each god. There were twelve principal deities in the Greek pantheon. Foremost was Zeus, the sky god and father of the gods, to whom the ox and the oak tree were sacred; his two brothers, Hades and Poseidon, reigned over the Underworld and the sea, respectively. Hera, Zeus’s sister and wife, was queen of the gods; she is frequently depicted wearing a tall crown, or polos. Wise Athena, the patron goddess of Athens , who typically appears in full armor with her aegis (a goatskin with a snaky fringe), helmet, and spear , was also the patroness of weaving and carpentry. The owl and the olive tree were sacred to her. Youthful Apollo , who is often represented with the kithara, was the god of music and prophecy. Judging from his many cult sites, he was one of the most important gods in Greek religion. His main sanctuary at Delphi, where Greeks came to ask questions of the oracle, was considered to be the center of the universe . Apollo’s twin sister Artemis, patroness of hunting, often carried a bow and quiver. Hermes , with his winged sandals and elaborate herald’s staff, the kerykeion, was the messenger god. Other important deities were Aphrodite, the goddess of love; Dionysos, the god of wine and theater; Ares, the god of war; and the lame Hephaistos, the god of metalworking. The ancient Greeks believed that Mount Olympus, the highest mountain in mainland Greece, was the home of the gods.
Ancient Greek religious practice, essentially conservative in nature, was based on time-honored observances, many rooted in the Bronze Age (3000–1050 B.C.), or even earlier. Although the Iliad and the Odyssey of Homer, believed to have been composed around the eighth century B.C., were powerful influences on Greek thought, the ancient Greeks had no single guiding work of scripture like the Jewish Torah, the Christian Bible, or the Muslim Qu’ran. Nor did they have a strict priestly caste. The relationship between human beings and deities was based on the concept of exchange: gods and goddesses were expected to give gifts. Votive offerings, which have been excavated from sanctuaries by the thousands, were a physical expression of thanks on the part of individual worshippers.
The Greeks worshipped in sanctuaries located, according to the nature of the particular deity, either within the city or in the countryside. A sanctuary was a well-defined sacred space set apart usually by an enclosure wall. This sacred precinct, also known as a temenos, contained the temple with a monumental cult image of the deity, an outdoor altar, statues and votive offerings to the gods, and often features of landscape such as sacred trees or springs. Many temples benefited from their natural surroundings, which helped to express the character of the divinities. For instance, the temple at Sounion dedicated to Poseidon, god of the sea, commands a spectacular view of the water on three sides, and the Parthenon on the rocky Athenian Akropolis celebrates the indomitable might of the goddess Athena.
The central ritual act in ancient Greece was animal sacrifice, especially of oxen, goats, and sheep. Sacrifices took place within the sanctuary, usually at an altar in front of the temple, with the assembled participants consuming the entrails and meat of the victim. Liquid offerings, or libations , were also commonly made. Religious festivals, literally feast days, filled the year. The four most famous festivals, each with its own procession, athletic competitions , and sacrifices, were held every four years at Olympia, Delphi, Nemea, and Isthmia. These Panhellenic festivals were attended by people from all over the Greek-speaking world. Many other festivals were celebrated locally, and in the case of mystery cults, such as the one at Eleusis near Athens, only initiates could participate.