The 'history' of the Holy Grail....

The Holy Grail is generally considered to be the cup from which Christ drank at the Last Supper and the one used by Joseph of Arimathea to catch his blood as he hung on the cross.

This significance, however, was introduced into the Arthurian legends by Robert de Boron in his verse romance Joseph d'Arimathie (sometimes also called Le Roman de l'Estoire dou Graal), which was probably written in the last decade of the twelfth century or the first couple of years of the thirteenth.

In earlier sources and in some later ones, the grail is something very different. The term "grail" comes from the Latin gradale, which meant a dish brought to the table during various stages (Latin "gradus") or courses of a meal. In Chrétien and other early writers, such a plate is intended by the term "grail." Chrétien, for example, speaks of "un graal," a grail or platter and thus not a unique item. Wolfram von Eschenbach's Parzival presents the grail as a stone which provides sustenance and prevents anyone who beholds it from dying within the week. In medieval romance, the grail was said to have been brought to Glastonbury in Britain by Joseph of Arimathea and his followers. In the time of Arthur, the quest for the Grail was the highest spiritual pursuit. For Chrétien, author of Perceval and his continuators (four works take up the task of completing the work that Chrétien left unfinished, two of which are anonymous, one is by Mannesier, and a fourth is by Gerbert de Montreuil), Perceval is the knight who must achieve the quest for the Grail. For other French authors, as for Malory, Galahad is the chief Grail knight, though others (Perceval and Bors in the Morte d'Arthur) do achieve the quest. Tennyson is perhaps the author who has the greatest influence on the conception of the Grail quest for the modern English-speaking world through his Idylls and his short poem "Sir Galahad". However, James Russell Lowell's "The Vision of Sir Launfal", one of the most popular of nineteenth-century American poems gave to generations a democratized notion of the Grail quest as something achievable by anyone who is truly charitable. The notion that the Grail story originated in fertility myths was popularized by Jessie Weston in her book From Ritual to Romance, which was used by T. S. Eliot in the writing of The Waste Land. Eliot's poem, in turn, influenced many of the important novelists of his and succeeding generations, including Hemingway and Fitzgerald.
I don't know if anyone has ever noticed (maybe this is an AO-première ) , but I have another explanation...

San Grail = Holy Grail

Mix up the letters a little, and you get

Sang Rail / Sang real = Real Blood (sang is French for blood)

Now tell THAT to the Pope