They built a well defended stone mole to enclose the harbour and ward off any naval attack, and they constructed a series of detatched forts, isolated block- houses first of timber and later of brick and stone, covering all the main avenues of approach, interspersed with obstacles and mines to obstruct any Moorish at- tack.4 This must be one of the earliest examples of the construction of interde- pendant detatched forts forming a ring well outside the central enceinte of a for- tress. For ill-considered economical and political reasons Tangier was aban- doned by the British in 1684 and her fortifications slighted.
British forces took the island of Minorca in 1708 and finally handed it back to Spain in 1802. During these years they were twice expelled and twice returned. On arrival they found Fort St. Philipe, a traditional square bastioned fort constructed in the sixteenth century, guarding the entrance to the magnifi- cent harbour at Port Mahon, supported by two fortlets. When built to Italian de- sign Fort St. Philipe was adequate to cover the entrance to the harbour and the vulnerable creek to the south, but, by the beginning of the eighteenth century, it was clear that it mounted insufficient artillery to dispute the passage of ships of the line and was vulnerable to a land attack. The British engineers therefore be- gan an elaborate process of augmenting the defences. Powerful lines of batteries were constructed close to the water's edge, the central fort was ringed by counterguards and a hornwork and a string of redoubts and lunettes was con- structed to cover the land approaches.
There is no space to describe in detail the defensive system of the eight- eenth century, but in essence it consisted of artificial barriers like ditches, sup- ported by enfilade fire from muskets and cannon from bastions and the outworks that ringed them. The Italian system of fortification had been developed system- atically by French engineers to a point when it could be carried little further. However, two important steps were taken by British engineers to improve the bastion system - the development of defensible caponiers which could pour dev- astating firepower on an enemy descending into the ditch, and the introduction of counterscarp galleries to take such an enemy in the rear. Both these features can be seen in the British works at Minorca and both were carried out before 1735.5 To augment the firepower of the coastal batteries when coping with the massed broadsides of ships of the line close in, a further device was adopted. The fougasse, a conical hole cut in the solid rock and packed with powder, pieces of iron and rocks, was grouped at the head of the peninsula and covering the waters of the vulnerable creek, to pour devastating showers of missiles upon any ship so foolhardy as to approach within range.6 These devices were installed during the final period of hectic rebuilding by the British between 1798 and 1802 when thirteen Martello towers, which predate those constructed on the coasts of Britain, were built by William Pasley.
By the end of the Napoleonic wars British attention was focussed on holding three positions on a permanent basis - Gibraltar, the cork in the bottle which