The fosse (defensive ditch)
In 1827 Eneas Mackenzie wrote: "The fosse or ditch that anciently surrounded the walls is now mostly filled up, and levelled with the adjoining ground. The space, however, which it occupied is still called the "King's Dikes." It appears to have been uniformly twenty-two yards in breadth, and is claimed by the corporation, to whom every waste within their jurisdiction devolves, by the authority of their charter. A narrow passage, which still remains open in many places, has also conducted round the town, on the inside of the wall, and was probably used for the purpose of conveying ammunition, during a siege."