e probably wrote his poem
between 1314 and 1321.

The Irish also produced another legend of this sort that was
enormously and universally popular, and became the chief authority on
the nature of heaven and hell, in the story of _Saint Patrick's
Purgatory_. Saint Patrick was said to have been granted a view of
heaven and hell, and a certain island in Lough Derg in Donegal was
reputed to be the spot in which he had begun his journey; and there,
it was said, those who desired to purge themselves of their sins
could enter as he had entered and come back to the world again,
provided their faith was strong enough.

This legend was probably known in Ireland from a very early time, but
it had spread over all western Europe by the twelfth century. Henry
of Saltrey, a Benedictine monk of the Abbey of that name in England,
wrote an account in Latin of the descent of an Irish soldier named
Owen into Saint Patrick's Purgatory in 1153; and this story soon
became the subject of poetic treatment all over Europe. We have
several French versions, one by the celebrated French poetess Marie
de France, who lived about 1200; and there are others in all the
languages of Europe, besides evidence of its wide circulation in the
original Latin. Its importance is shown by the fact that it is
mentioned by Matthew Paris, the chief English historian of the
thirteenth century, and also by Froissart, the well-known French
annalist of the fourteenth while Calderon, the great Spanish
dramatist, has written a play based on the legend. Dante undoubtedly
knew of Marie de France's version as well as the original of Henry of
Saltrey and probably others besides.

From what has been said it will be seen that Dante's masterpiece is
largely based on literature of Irish origin; but there are other
superlative exhibitions of human genius of which the same is true.
One of these is the story of Tristan and Isolde. Tristan is the
paragon of all knightly accomplishments, the most versatile figure in
the entire literature of chivalry; while Isolde is an Irish princess.
By a trick of fate these two drink a love potion inadvertently and
become irresistibly enamored of each other, although Isolde is
betrothed to King Mark of Cornwall, and Tristan is his nephew and
ambassador. The story that follows is infinitely varied, intensely
dramatic, delicately beautiful, and tenderly pathetic. It has been
treated by several poets of great genius, among them Gottfried of
Strassb