Castle of Campo Maior The Castle of Campo Maior ( ) is a medieval military fortification , in the civil parish of São João Bapista , municipality of Campo Maior , part of a first line of defense in the Portuguese Alentejo , oriented towards Spain , in conjunction with the military forts of Ouguela , Elvas , Olivença and Juromenha . It is a walled bulwark of the modern era , highlighted by a Renaissance - era window in the northern tower of the castle . It has been listed as a National monument since 1911 . History . Owing the regions occupation by successive tribes of Celts , Romans and Muslims , it is likely that the territory of Campo Maior has been settled during the pre - historic epochs . The land of Campo Maior was definitively conquered from the Moors by the forces of Kingdom of León in 1230 . The first foral ( " charter " ) was issued by the Bishop of Badajoz thirty years after this event . Eventually , the castle was conquered by the Portuguese in 1295 - 1296 , and integrated into the national territory in 1297 , under the Treaty of Alcanizes . In order to maintain the peace between Spain and Portugal , King Denis ordered the reconstruction of the fortress in 1310 , oriented toward his Iberian rivals . These fortifications were extended and rehabilitation during the 15th and 16th century completed , during the reigns of his successors John and Manuel , designed by Duarte d ' Armas . Kingdom . Around 1640 , following the Portuguese Restoration War , King John IV established a Counsel of War that formed their territory into military provinces : Minho , Trás - os - Montes , Beira , Estremadura , Alentejo and Algarve . Therefore , following the decision of John IV , work began in 1645 under the supervision of João Cosmander to reconstruct the bulwarks . Between 17th and 18th century the fortification was adapted for the time , obtaining the bulwarks and secondary walls , in addition to the installation of permanent military storehouses , stables and barracks . After 1644 , many of the reconstruction of the fortress was handled by Nicolau de Langres . A document , dated 14 May 1647 , identified Langres as the military engineer of the project , while requesting material for the construction of military square , in addition to the arms necessary to protect the castle and its surrounding territory . In 1662 , Luís Serrão Pimentel continued work on the walls . On 22 May 1680 , D . Peter , acting as regent , ordered Mateus do Couto , D . Diogo Pardo and António Rodrigues to Campo Maior , in order to verify the work being done on the citadel , under the plans of Luís Serrão Pimentel . During the Spanish War of Succession , in 1712 , the square was besieged by Spanish forces and defended in the main square . In 1732 , an explosion in powder magazine ( caused by thunderstorms ) resulted in the destruction of the castle and surrounding walls of the old town around 3 : 00 in the morning ; the space was totally levelled , and many of the homes around the walls were destroyed . At the time of the explosion , the magazine held of gunpowder and 5000 munitions ; the violent explosion resulted in a fire that , in addition to the direct deaths , consumed almost half of the towns homes . The powder magazine was reconstructed by order of John V of Portugal in 1735 , under the meticulous care of Manuel de Azevedo Fortes . On 2 July 1736 , Diogo Lopes de Sepúlveda was awarded the commission to the post of Sargent - Major , as part of his efforts in reconstructing the square after these events . But , in 1762 , Spanish forces , once again , invaded the territory ( during the Seven Years War and meeting the Portuguese in Campo Maior . Peninsular wars . During the Peninsular War , during the " Battle of the Oranges " ( ) , Portuguese forces capitulated in 1810 . After a small victory , these forces recapitulated in 1811 . 20th century . On 18 March 1911 , the structure was classified as a national monument by Decree . In the first hald of the 1940s , the " Direcção - Geral dos Edifícios e Monumentos Nacionais ( DGEMN ) " began works to restore the group of structures . A second phase of construction was began in the 1960s , and extended into the 1970s , marked by interventions in the castle walls and the Chapel of Nossa Senhora dos Aflitos . A third phase of reconstruction began in the latter part of the 1980s , when the castle and walls repaired , just before the castle became the responsibility of the Instituto Português do Património Arquitectónico " ( IPPAR ) , on 1 June 1992 , Decree - law 106F / 92 . Owing to bad weather in 2010 , the castle walls were partially destroyed . Architecture . The castle is located in an urban context , is walls encircling the area known as Outeiro de Santa Vitória , the top of which is the castle , in altitude , transformed into a citadel with bulwark fortifications . It is positioned , from the Spanish frontier and from Badajoz and Elvas ( areas that are visible from its towers ) , the fortress is encircled in the north , northeast , east and southeast by modern buildings and the town is similarly encircled by agricultural lands . A heavily walled fortification , formed of a ten - sided polygon curtain of walls , with some missing facades . The walls , from the south , in a clockwise direction : the bulwark of Boa Vista , middle bulwark of São Sebastião , the gates of the " Vila " ( " town " ) , the middle bulwark of Lisbon , middle bulwark of Curral dos Coelhos , bulwark of Santa Cruz , bulwark of Cavaleiro ( also referred to as the São João bulwark ) , the middle bulwark of Príncipe , bulwark of Fonte do Concelho , middle bulwark of São Francisco and middle bulwark of Santa Rosa . The fortification also includes a gap and counterescarp in part of its extension , namely in the south and northeastern parts , as well as four turrets . A number of military edifices have occupied the spaces within the castle , collectively maintaining several of the existing buildings in some form of use ( the warehouses , barracks , stables and living spaces ) . The castle retains two of its six original towers , an irregular rectangular space with walls forming a trapezoid space , with battlements and adarve permitting access to the remaining towers . The towers have battlements and walls , terminating in a frusto - pyramidal domes , rounded at the top . Each tower has a vaulted ceiling at the adarve , with the northern tower exemplified by a decorated Renaissance window . To the south , are the walls that circle the old village of Campo Maior , a rough design in the form of a elipse , with seven towers , six rectangular and one , in the northeast , octagonal , forming the main entrance to the complex . The walls are lower , in order to support barbettes and canon emplacements . One of the towers , in the southwest , along one of the false gates has battlements . To the southeast is , also , the Chapel of Senhor dos Aflitos . The castle grounds are semi - / permanently occupied by cultural ( museum historical and military architecture of Campo Maior ) ; residential ( part of the bulwarks occupied by residences , in the middle bulwark of São Sebastião there are gypsy communities ) ; and equipment ( part of the bulwarks occupied by storerooms and facilities for breeding of animals , as well as waste disposal ) .