Castle an Dinas was mentioned briefly by Richard Carew in his 1600s ‘Survey of Cornwall’:
Neere to Belowdy, commonly, & not vnproperly, termed Beelowzy, the top of a hill is enuironed with deep treble trenches, which leaue a large playne space in the midst: they call it Castellan Danis... and it seemeth (in times past) to haue bin a matter of moment, the rather, for that a great cawsey (now couered with grasse) doth lead vnto it.
Online courtesy of Project Gutenberg at
gutenberg.org/dirs/etext06/srvcr10.txt