More information : Centred at SV 88571605. OS and Admiralty air
photographs show the cropmark of a fortification extending
completely across Castle Down for 200 m.
On the ground it appears, for the most part, as a bank 2.5 m
wide and 0.2 m high with, occasionally, an outer or southward
facing ditch 1.5 m wide and 0.1 m deep.
It is clearly a setting out work with a massive south facing
bastion with orillons set in the centre of Castle Down plateau.
From it two 75.0 m lengths of walling would form an angle of
120. At the east end of the 'wall' there is a half bastion
from which a scarp extends northwards for 60.0 m along the
crest of the steep coastal slopes and ending at some
out-cropping rock. Going westwards from the main bastion for
75.0 m there are traces of another which seems to have been
unfinished in its setting out. Its plan, however, would, of
necessity have been distorted since it is on the lip of the
coastal slopes at this side of the island. There is a gap of
30.0 m and then a flanking scarp, similar to that on the east
but slightly below the crest of the plateau, can be traced for
60.0 m towards the 16th century, mis-named, King Charles'
Castle. The flanking scarp ceases near a small quarry pit.
This unfinished and previously unrecorded fortification would
have enclosed some 36 hectares of the north part of Tresco.
Commenting on the earthwork Mr A D Saunders says the work
"is clearly 16th century in form. The shape of the bastions
suggests it could belong to the 1550's, contemporary with
Harry's Walls, and designed as an outwork to King Charles
Castle".
Surveyed at 1:10 000 on PFD and at 1:1250. (1a-c)
The outwork is described and the historical associations
noted. (2)
Scheduled. (3)
As depicted on the AM, this is a very slight work, the bank up to 0.5m high in places but mostly no more than 0.3, the ditch (where it exists) no more than 0.2m deep. It is placed in a reverse slope position to surprise any attacker, though if built to full height this aspect would have been compromised. The obtuse-angled bastions with orillons suggest that it is contemporary with King Charles' Castle or only slightly later. (4-5)
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