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conflict was delimited by the towns of Badajoz (34, 35), Elvas (243, 28), Campo Maior (27) and Olivenza (26), the heart of the border throughout this long war. The strategic value of these and other towns in their area of influence, such as Telena (51), Vila Viçosa (244, 245), Estremoz (4), Ouguela (246) or Juromenha (247) explains the large number of related documents: 18 plans in all, representing valuable graphic testimony of the fortifications and defensive tactics of the military strongholds of both Portugal and Extremadura which played such an important role in the conflict. From the 1650’s on, after the reincorporation of Catalonia, the Portuguese front was active in this area. In 1657, the Royal Army of Extremadura conducted a great campaign ending in the conquest of Olivenza (26) and Mourão (248), a campaign that led Portugal to respond the following year with a siege on Badajoz, the key stronghold of Extremadura. The attack lasted for five months before it was finally repelled by Luis Méndez de Haro, the chief minister of Philip IV (249, 23, 22). In its retreat, the Portuguese army was pursued by the Castilians who, after crossing the border via the Caya river, held Elvas under siege for just over two months. This military action ended in the “Battle of the Lines of Elvas”, in which the Portuguese troops obtained the first great victory of the Restoration (25).

The third area, the northern stretch of the border, gained in importance towards the end of the conflict, especially when the Portuguese army occupied Valencia de Alcántara (1664), a vital position which forced the Spanish government to optimise the defence of this stretch of border, delimited by Valencia de Alcántara itself and the towns of Alcántara and Moraleja. Plans 5, 6, 7 and 8 refer to these towns.