Given how ubiquitous stories and images of the Holy Grail are, you'd be forgiven for thinking that this mysterious vessel--which, according to legends, was said to have held the blood of Christ--has been part of Christianity since the earliest days of the church. In truth, however, the Holy Grail was a product of the Middle Ages, when it became the subject of a favorite story. Today, the very words "Holy Grail" conjure up images of medieval knights in King Arthur's court or Indiana Jones choosing the correct goblet. What these have in common, of course, is that they're fictional stories. So the first thing to remember about Grail narratives is that they were never intended to be anything more than just that, stories.
No one went on a "quest for the Holy Grail" during the Middle Ages except the fictional knights of King Arthur's Round Table, who are celebrated in poetry and romance. Although some people identify the legendary Grail with the chalice that Jesus used at the Last Supper, the medieval authors of the Grail story made it clear that the two vessels were not the same. In any event, there were already several actual chalices on display in medieval churches which were thought to be relics of the Last Supper. There is also no evidence connecting the Grail to Mary Magdalene, as Dan Brown does in "The Da Vinci Code." If anything, some scholars argue, the Grail was associated with the Virgin Mary, the mother of Jesus.
The Grail legend began as a long narrative poem in French titled "Conte du Graal" ("Story of the Grail") by the 12th-century poet Chrétien de Troyes. (Troyes is in northern France, near Paris). Like other French poets of his time, Chrétien wrote mostly about the knights of King Arthur's court. The poets claimed that the stories they told came from Brittany, where some of the Celts who once lived in Britain had fled across the English Channel when the Angles and Saxons invaded during the sixth century—although no modern scholar has found any Celtic tales of Arthur that predate the French versions.
The hero of Chrétien's poem is Perceval, a young man whose mother has raised him in the forests of Wales, far from Arthur's court, because she wants to protect him from the fate of his brothers, knights who have died in battle. Perceval accidentally comes across a knight and wants to be one, too, and so he leaves home on a quest.. Perceval is an innocent, in a good sense—he is kind and brave—and also in a bad sense, for he knows nothing about civilization, chivalry, or even Christianity. One day he meets a fisherman who turns out to be a king and invites him to his castle.
While they are at dinner, a young man walks through the hall carrying a lance from whose tip runs blood, followed by a maiden holding what Chrétien calls a "graal," which he says is made of gold and emits its own light. Chrétien describes the "graal" as big enough to hold a fish, although (as Perceval learns later) it actually holds a eucharistic host.
Medieval Christians would immediately connect the lance with Christ's passion (his body was pierced with a lance after his death) and the "graal" in some way with the Mass, but Perceval is ignorant of these allusions and does not ask. When he awakes the next morning, the castle is empty and the Fisher King has disappeared. Perceval spends a full five years wandering under a curse, until, with the help of a hermit, he confesses his sins and learns about Christ. Unfortunately, Chrétien died in around 1190 before finishing his poem, so we never find out what happens to Perceval after that.
It seems clear from Chrétien's poem that he was not sure exactly what a "graal" was. It is not a Celtic word. Instead, it seems to have originated in the languages spoken in the Pyrenees region bridging France and Spain, where there are records of domestic dishes of some sort called "gradales" and "gradals." The word might be related to the Latin adjective "gradalis" ("in stages") and refer to the courses in a meal, or to the Catalan noun "gresa" for potter's clay.