Within the _caer_ were circular stone beehive huts; also chambers that were circular were contrived in the thickness of the walls. These "sentry boxes" have been noticed in Wales, and also in Cornwall and Devon. The account of Castel-an-Dinas, before it was robbed for the erection of a tower, is precisely such as might be given of one of those in Ireland or Wales:-- "It consisted of two stone walls, one within the other, in a circular form, surrounding the area of the hill. The ruins are now fallen on each side of the walls, and show the work to have been of great height and thickness. There was also a third or outer wall built more than half-way round. Within these walls are many little enclosures of a circular form, about seven yards in diameter, with little walls round them of two or three feet high; they appear to have been so many huts for the shelter of the garrison." In fact, this was a royal dinas. Not only had it the requisite double wall, but also the _drecht gialnai_, or dyke of the hostages. Every king retained about him pledges from the under-chiefs that they would be faithful. There are several of these stone camps in Devon and Cornwall. In Somersetshire Whorlebury is very interesting; in Devon are Whit Tor and Cranbrook; in Cornwall the Cheesewring camp, Carn Brea, Chun Castle, the camp of Caer Conan on Tregonning Hill, Helborough, beside Castel-an-Dinas in Ludgvan. The heroic legends of Ireland attribute these stone camps to the Firbolgs, the non-Aryan dusky race that was in possession previous to the arrival of the Celts. But that the Milesians learned from them the art of constructing such castles is very certain, for in Christian times the monks imitated them in some of their settlements. Lord Dunraven, who has photographed these stone duns, says:--