Ticknor prefers it to the more celebrated "Devotion of the Cross,"
and says that it "is commonly ranked among the best religious plays
of the Spanish theatre in the seventeenth century."

In all that relates to the famous cave known through the middle ages
as the "Purgatory of Saint Patrick", as well as the Story of Luis
Enius -- the Owain Miles of Ancient English poetry -- Calderon was
entirely indebted to the little volume published at Madrid, in 1627,
by Juan Perez de Montalvan, entitled "Vida y Purgatorio de San
Patricio". This singular work met with immense success. It went
through innumerable editions, and continues to be reprinted in Spain
as a chap-book, down to the present day. I have the fifth impression
"improved and enlarged by the author himself," Madrid, 1628, the year
after its first appearance: also a later edition, Madrid, 1664. As
early as 1637 a French translation appeared at Brussels by "F. A. S.
Chartreux, a Bruxelles." In 1642 a second French translation was
published at Troyes, by "R. P. Francois Bouillon, de l'Ordre de S.
Francois, et Bachelier de Theologie." Mr. Thomas Wright in his
"Essay on St. Patrick's Purgatory," London, 1844, makes the singular
mistake of supposing that Bouillon's "Histoire de la Vie et
Purgatoire de S. Patrice" was founded on the drama of Calderon, it
being simply a translation of Montalvan's "Vida y Purgatorio," from
which, like itself, Calderon's play was derived. Among other
translations of Montalvan's work may be mentioned one in Dutch
(Brussels, 1668) and one in Portuguese (Lisbon, 1738). It was also
translated into German and Italian, but I find no mention of an
English version. For this reason I have thought that a few extracts
might be interesting, as showing how closely Calderon adhered even to
the language of his predecessor.