Saint George and the Dragon

Paulo Uccello, Saint George and the Dragon, 1470

In the well-known version from Jacobus de Voragine's Legenda aurea (The Golden Legend, 1260s), the narrative episode of Saint George and the Dragon took place somewhere he called "Silene" in what in medieval times was referred to as "Libya" (basically anywhere in North Africa, west of the Nile). Silene was being plagued by a venom-spewing dragon dwelling in a nearby pond, poisoning the countryside. To prevent it from affecting the city itself, the people offered it two sheep daily, then a man and a sheep, and finally their children and youths, chosen by lottery. One time the lot fell on the king's daughter. The king offered all his gold and silver to have his daughter spared, but the people refused. The daughter was sent out to the lake, dressed as a bride, to be fed to the dragon.

Saint George arrived at the spot. The princess tried to send him away, but he vowed to remain. The dragon emerged from the pond while they were conversing. Saint George made the Sign of the Cross and charged it on horseback, seriously wounding it with his lance. He then called to the princess to throw him her girdle (zona), and he put it around the dragon's neck. Wherever she walked, the dragon followed the girl like a "meek beast" on a leash.

The princess and Saint George led the dragon back to the city of Silene, where it terrified the population. Saint George offered to kill the dragon if they consented to become Christians and be baptized. Fifteen thousand men including the king of Silene converted to Christianity. George then killed the dragon, beheading it with his sword, and the body was carted out of the city on four ox-carts. The king built a church to the Blessed Virgin Mary and Saint George on the site where the dragon died and a spring flowed from its altar with water that cured all disease. Only the Latin version involves the saint striking the dragon with the spear, before killing it with the sword.

—Wikipedia

 René Guénon interprets the slaying of the dragon this way:

Victory over the dragon has, as its immediate consequence, the conquest of immortality, which is represented by some object the approach to which is guarded by the dragon; and this conquest essentially implies the reintegration into the centre of the human state, that is, into the point where communication is established with the higher states of the being. (Fundamental Symbols: The Universal Language of Sacred Science)

The water in the lake guarded by the dragon would then be the water of life. The victory over the dragon would have initiatory meaning.

There seems to be also a residue in this legend of some hierogamic ritual (the princess dressed as bride) that has been reinterpreted in the Christian context as union with a loathsome beast.