Though man usually makes his gods in his own image, they are unlike as well as like him. Intermediate between them and man are ideal heroes whose parentage is partly divine, and who may themselves have been gods. One mark of the Celtic gods is their great stature. No house could contain Bran, and certain divine people of Elysium who appeared to Fionn had rings "as thick as a three-ox goad."[516] Even the Fians are giants, and the skull of one of them could contain several men. The gods have also the attribute of invisibility, and are only seen by those to whom they wish to disclose themselves, or they have the power of concealing themselves in a magic mist. When they appear to mortals it is usually in mortal guise, sometimes in the form of a particular person, but they can also transform themselves into animal shapes, often that of birds. The animal names of certain divinities show that they had once been animals pure and simple, but when they became anthropomorphic, myths would arise telling how they had appeared to men in these animal shapes. This, in part, accounts for these transformation myths. The gods are also immortal, though in myth we hear of their deaths. The Tuatha Dé Danann are "unfading," their "duration is perennial."[517] This immortality is sometimes an inherent quality; sometimes it is the result of eating immortal food--Manannan's swine, Goibniu's feast of age and his immortal ale, or the apples of Elysium. The stories telling of the deaths of the gods in the annalists may be based on old myths in which they were said to die, these myths being connected with ritual acts in which the human representatives of gods were slain. Such rites were an inherent part of Celtic religion. Elsewhere the ritual of gods like Osiris or Adonis, based on their functions as gods of vegetation, was connected with elaborate myths telling of their death and revival. Something akin to this may have occurred among the Celts.