Mr. Richard Edmonds remarks that "Treryn Castle, Maen Castle, Chûn Castle, Castle-an-Dinas, and several other cliff-castles, and hill-castles, in the Land's End district, have been in existence probably between two and three thousand years. And Treryn Castle, with its high massive vallum, deep ditch, and the foundations of its stone wall, twelve feet thick, presents so little temptation either to the agriculturist or to the builder, that its existing remains, vast as they are, need no Society's protection for their continued duration for generations yet to come.
All castles, of course, do, or did once contain dwellings of some kind for their occupants. But the low huts which once stood within the castles near Penzance (although considerable remains of such dwellings in Chûn Castle were extant in Borlase's time) have now almost everywhere disappeared. It was not, however, from these rude huts, but from the fortifications enclosing them, that our very ancient castles derived their name; and not one of them, at the present day, appears more worthy of being thus called than at Treryn Castle."
"I cannot tell how the truth may be, I say the tale as 'twas said to me." SCOTT.
Old traditions say that the headlands of Castle Treen, or rather Trereen, on which the Logan Rock carn and adjacent crags stand, was raised out of the sea by enchantment. This portion of the stronghold, enclosed by the inner line of defence, running directly across the isthmus, is generally spoken of as _The Castle_, and that between it and the outer or landward embankments is usually called Treen Dynas.
It is not known what powerful magician raised this giant's hold, though it was believed that its security depended on a magic stone called "the key of the Castle," respecting which Merlin had something to say, as well as about many other remarkable stones in the neighbourhood. Castle Treen, however, must have stood where it is long before Arthur and his magician visited West Cornwall.
The key was an egg-shaped stone, between two and three feet long, which was contained in the cavity of a rock with a hole facing the sea, through which it might be turned round; and the opening appeared large enough for it to be passed through. Many attempted to get it out, but they always found it to hitch somewhere; and lucky (according to old folks' faith) that it did, because the sage Merlin prophecied that when the key of the Castle was taken out of the hole, Men Amber (the holy rock) would be overthrown, the Castle sink beneath the ocean, and other calamities occur.