Bayonne has been inhabited since roman times, when it was known as Lapurdum. Its medieval fortifications were improved by Louis XII, and Francois I, enabling the town to defend itself against a Spanish army in 1523.
Vauban visited Bayonne sometime in the 1670's, and planned more improvements to the fortifications, including the construction of additional demi-lunes and a large, quadrangular citadel to the north of the river Adour. The city itself, which lies to the south of the Adour and is bisected by the river Nive, was surrounded by a wall of 9 rather eccentric bastions.
The citadel was designed from scratch by Vauban, and is a large square work with four bastions. It saw action against the invading British forces at the end of the Peninsular War, when it was taken by General Hill after a determined defence by the French.
The fortifications of Petit Bayonne, the eastern half of the town, had four bastions and one gate, the Porte de Notre Dame. To the west, Grand Bayonne had five bastions and two gates, the Porte d'Espagne and the Porte de la Poterne. The first gate is unusual in that it enters the walls through a bastion, not through the courtine as is normally the case.
The size and shape of each bastion is very different, and there are varying lengths between them, which makes the fortifications seem less regular than some. This is probably due to the way Bayonne was fortified in several stages, with improvements added gradually.
References:The Broch of Clickimin is a large and well preserved, though somewhat restored broch near Lerwick. Originally built on an island in Clickimin Loch (now increased in size by silting and drainage), it was approached by a stone causeway. The water-level in the loch was reduced in 1874, leaving the broch high and dry. The broch is situated within a walled enclosure and, unusually for brochs, features a large 'blockhouse' between the opening in the enclosure and the broch itself. Another unusual feature is a stone slab featuring sculptured footprints, located in the causeway which approached the site. Situated across the loch is the Clickimin Leisure Centre.