A chain of defences

I've been collecting  some old postcards of Guernsey and a number feature Martello towers. The landscape on these two is quite populated with them and the chain-like siting formation is evident. They are almost like a 19th Century British version of the Atlantik Wall.  I think the Guernsey ones are mainly sturdy granite whereas the East coast ones are possibly brick and rendering, but both with pretty thick walls. The Bunker-like role of unseen observer surveying the landscape recurrs as does the intensifying effect of viewing the world through a narrow aperture or loop-hole. I like the romance of the idea that Martello is a corruption of Motella, so named because of the myrtle growing round about the tower in Corsica.