To describe the festival(s), we must first look at the worship of Asklēpiós, and the buildings that bore the same names as the festival. Asklēpiós was, and is, a much beloved Theos. He started out being honored as a hero--most notably in the Iliad--where his sons joined the battlefield of Troy as 'son(s) of the great healer Asklēpiós'. According to (amongst others) the Homeric Hymns, he was born as the son of Apollon and Koronis:
"I begin to sing of Asklepios, son of Apollon and healer of sicknesses. In the Dotian plain fair Koronis, daughter of King Phlegyas, bare him, a great joy to men, a soother of cruel pangs. And so hail to you, lord: in my song I make my prayer to thee!"
It seems Asklēpiós was such a fine healer, he could even bring the dead back to life. As dominion over the dead lies firmly in the hands of the Theoi, Zeus struck Asklēpiós with a lightning bolt, but placed his image into the sky as the constellation Ophiochus. This event also led to His apotheosis--his deification--and from that point on, around 400 BC, He was worshipped both as hero and Theos, or sometimes only one of two.
Worship places of Asklēpiós were called 'asklepieia' (Ἀσκληπίεια). An asklepieion (Ἀσκληπιεῖον) served as a temple, a hospital, and as a training-institute of the healing arts. The most famous of all the asklepieia was located at Epidaurus, and large parts of it are preserved. The site is open to visitors. In ancient Hellas, the sick would come to an asklepieion and offer a sacrifice to Asklēpiós--amongst the recorded sacrifices are black goats or sheep, gold, silver, or marble sculptures of the body part that required healing, and coins--in hopes of healing. They would then settle into the abaton (άβατον) or enkoimeterion (εγκοιμητήριοn), a restricted sleeping hall, which was occupied by the sick alone, or sometimes by a group of them, as well as a good few snakes.
Snakes are considered sacred animals of Asklēpiós, and they promote healing. Our modern symbol of medication and healing, the asklepian, still shows this. The species of snakes found in the temple, on the grounds, and in the abaton were most likely Zamenis Longissimus, also known as the Aesculapian Snake. They can grow to a length of up to two meters, and are non-poisonous.
The sick would spend the night at the abaton, and would receive counsel from Asklēpiós Himself in his or her dreams, during an induced sleep known as 'incubation', or 'enkoimesis' (ενκοίμησις), where the patient drifts between waking and sleeping, and is said to be susceptible to messages of the Gods. If the god did not visit the patient the first night, incubation was continued on following nights. Asklēpiós would either heal the supplicant directly in the dream state, or tell him what to do to cure his illness or affliction. The priests listened to the dream, as described by the patient, and would divine the meaning of the Theos from it. As such, all healers were also master dream interpreters who would divine the treatment to be followed from the patient's account of the dream. Treatment often consisted of supplication, fasting, a special diet, meditation or prayer. There are accounts of surgeries having taken place at the asklepieia as well.
As for the festival of Asklepieia: there are two incarnations of it, the regular Asklepieia, and the Asklepieia Megala (Μεγάλα Ασκληπιεία). The Asklepieia Megala, or 'greater Asklepieia', was a huge event, and part of the pan-Hellenic games. In 242 BC, during the Mercenary War, the sanctuary at Epidaurus was granted immunity from war, and the Asklepieia Megala was established as a festival of athletic and musical competitions, held every four years, for a nine day period. Theater performances were also a huge part of the festival, and the famous theater of Epidaurus still stands today, one of the seven wonders of ancient Hellas.
The first of the festival days was spent preparing for the actual festival. The second day, religious exercises were undertaken. All temples and shrines were richly decorated and sacrifices were made to Apollon, Asklēpiós, Artemis, and Leto. Perhaps and the children of Asklēpiós--Hygieia (health, cleanliness, and sanitation), Iaso (recuperation from illness), Aceso (the healing process), Aglaea (beauty, splendor, glory, magnificence, and adornment), and Panakea (universal remedy)--also received sacrifice. Apollon received the first offering along with Asklēpiós: a cock, the fowl associated with Asklēpiós. They also received barley meal, wheat, and wine. Asklēpiós was then gifted a bull, a second bull was sacrificed to His male associates, and a cow to His female associates.
On the eve of the third day, a statue of Asklēpiós was driven through the precinct, and followed by torch-bearers and priests, who sung hymns to Him. The priests sang and spoke the praise of the Theos. There were vigils throughout the night, and during the daylight hours of the third day, there were feasts. The succeeding days were given up to athletic contests in the stadium, races, wrestling contests, singing contests and theater performances.
The Asklepieia Megala was only held at Epidaurus; all other asklepieia--as well as at Epidausus the other three years--held only a small ceremony for the Theos. The festival did not include athletic games outside of the Asklepieia Megala, but there might have been a focus on singing, and there might have been large banquets, held after sacrifices were made to the Theos.
Today, we should be reminded that doctors take the Hippocratic Oath, even if it was edited, and that all doctors are the hands of Asklēpiós. If you were putting off a doctor's or dentist's appointment, this is the day to plan them on. It is, of course, encouraged to give sacrifice to Asklēpiós and seek His guidance for all doctors and those in the medical profession, as well as our own health, and that of those around us. If you are struggling with your health, sacrifice to Asklēpiós and ask for Him to come to you in your dreams on this night. Note down your dreams in the morning (and of subsequent mornings, if you did not receive an oracular dream), and see if you can gleam a solution to your problems from them. This day is also a good day to fast, or to eat very healthy. Perhaps you can make a promise to yourself to eat healthier, or go to the gym more often. Think of your health and how you can stimulate it.
Image source: asklepian.