Based on a very clearly defined line, the walls were built up with unworked stone - orange-coloured granite that is also very prominent on the side turrets. The wide joints between them are filled with wedges of a smaller size. Some of the holes you can see in the joints are deliberate and have been left there for the city’s large colony of swifts to build their nests.
The top of the walls is crowned by rows of merlons built in masonry work. Most of them were levelled off with a small double-sided roof during restoration work at the beginning of the 20th century