... He has many castles, two of which, "Valachin" (i.e. Evalach-in) and Tarabel (in the French "Carabel," a corruption of some such name as Caer Aval), bore his own name.  The approach to Castle Valachin, by a gate over a river an arrow-flight broad, where scarce two chariots could pass, is also characteristic of the entrance to the abode of the dead.
    Much of the first part of the Grand St. Graal is taken up with an account of Evalach's (Avallach's) wars with Tholome, King of Egypt.  Geoffrey of Monmouth tells of one Bartholomeus who warred against Spain.  Both Spain and Egypt are alike to be located in the region of the departed, together with Orkauz or Orcanz (Orkney), one of the cities of Evalach, while the whole expedition may be regarded as one more version of the Harrying of Hades.
    The form of the name "Mordrains" given in Manessier's portion of the Conte del Graal is "Noodran," which Professor Rhys suggests is a misreading of Guitnev, a form of Gwyddno, the name of the Fisher in the Taliessin story, the father of Elphin.
    The name Mordrains is represented in the Grand St. Graal as having been given to Evalach when he was baptized by Joseph.  This may either mean that in the older tales, which the romancer was endeavouring to adapt to the record of Joseph's missionary triumphs, Gwyddno and Avallach were different names for the same personage, or that they were different personages, whom he connected together by this simple expedient.  From what we have already learnt as to the difficulty of distinguishing the roles of the Celtic Divinities of the Underworld, an explanation which meets both these suppositions probably comes nearest to the truth.
    What is most important for our present purpose is to notice that a very large part of the Grand St. Graal is taken up with the travels of Mordrains, or Avallach, Lord of the Underworld, and those connected with him, from one island to another; that some of those islands have features which strongly recall the islands of Bran or Brandan's wanderings in his thirst for the souls of men.
    Chief among these is the Turning Island.  In Welsh Literature, one of the names for the abode of the dead is "Caer Sidi," which Professor Rhys renders "the Spinning or revolving Castle."...(The Legend of the Holy Grail, its Sources, Character and Development, Kempe, 1905)