In 1806 great alterations were made on the edifice. The north and south transepts were removed, new and wider aisles were built on each side of the nave, and the outer walls of the aisles were carried to such a height that the whole nave could be covered with a roof of one span (Fig. 608), “thus totally eclipsing the beautiful windows in the nave, and covering up the handsome carved cornice of the nail-head quatrefoil description which ran under the eaves of the nave.”[73] The windows of the clerestory (three on each side), which are now concealed by the roof, are peculiar in their arrangement, being placed over the piers instead of over the centre of the arches, as is usual. Externally they have plain splays, and internally they seem to have been richer, but are now obscured by plaster. The windows and the dog-toothed cornice seem to point to an early date. [Illustration: FIG. 608.--Brechin Cathedral. View from South-East.] The only parts of the interior of the nave spared during the above restoration are the main piers, of which there are eight (Fig. 609), with four responds. Two of these piers seem to indicate, from their form, so far as not damaged, that this part of the structure must originally have been of first pointed work. The piers on the south side are octagonal, and those on the north side are alternately octagonal and clustered. A remarkable feature of the building is observed in connection with these piers, those of the south side, together with the arcade above them, being considerably thinner than those of the corresponding parts of the north side. As the clerestory walls above are the same on both sides, it is difficult to account for the difference in size of the piers. The interior of the nave is 83 feet 6 inches in length by 57 feet 6 inches in breadth. Fortunately part of the west end has not been interfered with, [Illustration: FIG. 609.--Brechin Cathedral. Plan.] [Illustration: FIG. 610.--Brechin Cathedral. West End.] notwithstanding all the alterations, and there we still have the original transition doorway, flanked by the fifteenth century tower on the north, and the famous round tower on the south (Fig. 610). At the east end of the nave are preserved portions of the ruined side walls of the aisleless choir, a beautiful example of first pointed work (Fig. 611). [Illustration: FIG. 611.--Brechin Cathedral. Choir.] The most interesting, as well as the most ancient, structure connected with Brechin Cathedral is the round tower, 103 feet in height, which is now incorporated with it, and occupies the place of a spire at the south-west angle (see Figs. 608 and 610). This and the corresponding round tower at Abernethy,[74] on the south side of the Tay, are the only representatives on the mainland of Scotland of this special kind of erection. At Egilsay, in Orkney,[75] is found the only other round tower of this kind in the country.