[From Castle Rushen, Armitage Rigby, 1927]
HE curtain or enceinte wall rises from the scarp of the ravine or ditch surrounding the Castle, in an irregular octagonal form. As before pointed out, one reason for this form would seem to have been the desire to follow approximately the very unusual shape of the inner ward, in accordance with the principles of concentric planning. Another equally important reason was undoubtedly the lie of the ground. The hummock of boulder clay, on the apex of which the original tower was erected, is a flattened cone. Next to a circle, which has disadvantages, a many-sided figure would best suit the situation, and in this case an octagon fitted the circumstances admirably. The towers at the angles give excellent command of every part of the wall as well as the scarp of the ditch, so that an attempt to undermine i t would seem to be almost out of the question. That such an attempt, however, w as considered within the bounds of possibility is strewn by the care with which the base of the wall was protected. The protection cat insisted of a sloping plinth formed of what the French call beton, a mixture which is still much used for building in parts of France. It consists of a strong lime mortar mixed with stones, and as it sets very hard it would form a fine protection against undermining. Most of this plinth is now buried by the filling in of the ravine, and the part exposed to view in the Northern part of the " Moat" is much broken. A considerable amount of it was hacked away with great difficulty during the recent excavations, as it was mistaken for an accidental accumulation of mortar.
The alure or parapet walk on the curtain wall was originally continuous over the whole length of the wall and completely encircled the main ward except where the Gate House intervened. Portions of it near the entrance have since been altered and included in later buildings connected with Lord Derby's house and the Court room. Before these alterations were made it continued over the entrance arch of the Gate House and along the wall of the entrance passage as far as the barrier, thus allowing a large body of men to be posted in excellent command of the approach, though we may doubt the opinion of the author of " Brittannica Curiosa," who says, " In case of an attack ten thousand men might be destroyed by a very few in attempting to enter." The portion over the entrance was probably machicolated like the part above the sally port.
One of the embrasures of the curtain wall still shews holes for the trunnions of a shutter which was hung in position like a towel roller. This gave protection against the bolts of the besiegers while the defending archerwas loading. What was the approved method of holding it open when ready to shoot is not so clear, but there are several ways in which it might be done.
There is now an inner wall to the parapet which is either an addition or a rebuilding of an earlier one. The masonry differs considerably from the rest. There seems to have been no rule on this point. Such parapets are found within and without the inner wall.
In pictures of about the end of the 17th century the towers on this wall are strewn with steep tripped roofs and overhanging eaves. It would, however, seem more likely that the roofs were originally flat to give accommodation for bowmen. In towers of larger area it was usual to have gabled or pyramidal roofs kept well within the parapet, leaving room for men to stand between the foot of the roof and the parapet, but in such small towers that was almost impossible.
It should be noted that the curtain wall was built in three sections. The first of these was erected at the same time as the Gate House, and before the enlargement of the inner ward. This portion was finished off apparently without any intention of immediately continuing the wall as it turned in to join the tower, and no bond was left.
The second section was to point D, but in this case there was no intention of stopping, as the end of the wall was left in steps, and the upper portion was built continuously with that of the third section.
The third section joined the first at point E, where bond seems to have been left.
In each of these sections the towers are of different design. Indeed in the first section they are not strictly towers, but turrets corbelled out from the wall.
In the second section the towers rise from the scarp and are corbelled out to larger size above where they contain chambers entered from the parapet.
In the third section the towers are of greater size, and the same size throughout their height and contain rooms on three stories.
There are no loops in the first section, and those in the second and third are different.
In spite of the differences noticeable, it is improbable that the building of this wall in sections points to change of plan. The definite stoppage at point C probably indicates a want of ready money or fear of an attack, in either of which cases a portion completed may have been considered better than a greater length half built. The last section may well have been left for the convenience of taking in stone for the building of the inner ward. The varying height of the curtain wall probably accounts for the differences in the construction of the towers, while the different designs of loops may merely show that freestone had become scarce as the Castle neared completion.
* The plans left by Mr. Rigby do not indicate these points.