The legend says that the village was founded by several heads of family who lived dispersed in the countryside and decided to group together for greater protection. Discovering an open space, one says to the others: “Here the field is bigger”. Traces of different origins allow us to conclude that the present territory of the municipality of Campo Maior has been inhabited since Prehistoric times.
It was certainly a Roman settlement, dominated by Moors for half a millennium and conquered by Christian knights of the Pérez de Badajoz family in 1219, who later offered the village belonging to the municipality of Badajoz to the Church of Santa Maria do Castelo.
On May 31, 1255, D. Afonso X, king of Leão, elevated it to Vila.
Senhor da Vila, Bishop D. Frei Pedro Pérez grants, in 1260, the first charter to its residents as well as the following coat of arms: N. Sr.ª with a lamb, and the caption “Sigillum Capituli Pacensis”.
On May 31, 1297, through the Alcanizes Peace Treaty signed in Castile by D. Fernando IV, king of Leão and Castela and D. Dinis, it became part of Portugal, together with Olivença and Ouguela.
Campo Maior will successively belong to D. Branca, sister of D. Dinis, in 1301; D. Afonso Sanches, illegitimate son of the same king, in 1312; and again to King D. Dinis in 1318.
Its castle that rises to the east of the village was rebuilt by D. Dinis in 1310, and it was in the 17th and 18th centuries that fortifications were built, making Campo Maior an important stronghold in Portugal.
As a reflection of the Castilian influence in Campo Maior, during the Revolution of 1383-85, the military garrison and the inhabitants of the village placed themselves next to the king of Castile, making it necessary that King D. João I of Portugal and D Nuno Álvares Pereira moved purposefully to the Alentejo with his armies to surround it for more than a month and a half and occupy it by force, at the end of 1388.
In 1512, King D. Manuel I granted a charter to the village of Campo Maior.
Since the end of the 15th century, many of those persecuted by the Inquisition in Castile have taken refuge in Portugal. The population of Campo Maior will increase substantially at the expense of the residence of many of these fugitives.
The Jewish community or labeled as such was so numerous in the village in the 16th century that in the lists of those presented in acts of faith carried out in Évora by the Inquisition, Campo Maior appears among the lands of Alentejo with the highest number of accused of Judaism.
The war with Castile from 1640 will produce the first major transformations.
The need to fortify the village that during the past three centuries had developed sharply outside the medieval fence, the urgency to build a new walled belt to defend the residents of the new village against attacks by the Castilian armies, will compel the king to send large amounts in cash, military engineers, skilled workers and employ a large contingent of unskilled personnel. The military contingents are then numerous. It is estimated that in the second half of the 17th century, for every four people living in the village, one was in the military. Campo Maior was, for some time, the main headquarters of the Dutch mercenary troops deployed to the Alentejo. At that time the village became the most important military center in Alentejo, after Elvas.
In 1712, the Castle of Campo Maior was surrounded by a large Spanish army commanded by the Marquis de Bay, who for 36 days dropped tons of bombs and shrapnel on the village, having managed to open a breach in one of the ramparts; the invader, intending to enter there, suffers heavy casualties that force him to lift the siege.
On September 16, 1732, at three in the morning, a violent thunderstorm broke out, the magazine, containing 6000 arrobas of gunpowder and 5000 ammunition, located in the big tower of the castle, struck by lightning, immediately triggering a violent explosion and a fire that dragged about two thirds of the population.
D. João V determines the rapid reconstruction of the castle. The village will slowly rise from the ruins and gradually rebuild itself to return to the first place in times of war and a place of commercial exchange and peaceful relations with the neighboring peoples of Spain, in times of peace.
In the 18th century, the construction of the current Churches of Misericórdia and Matriz ended, and the first stone was laid for the founding of the Church of S. João. Expectation and São João Baptista, in 1766.
The first years of the 19th century are in Campo Maior of great agitation. A siege in 1801 by the Spanish and a local revolution in 1808 against the French who then invaded Portugal prove this.
The Campo Maior uprising against the Napoleonic occupation will be victorious due to the support of the Badajoz army that remains in the village for about three years.
In 1811, a new French invasion arose that closed the village for a month, forcing it to capitulate. But its resistance was such that it gave time for the Luso-British reinforcements to arrive under the command of Beresford, who put the French in disarray, and the village then won the title of Vila Leal and Valorosa, a title present in the current coat of arms of village.
The struggles between liberals and absolutists in Campo Maior are also remarkable events.
“Morbid cholera” kills, in 1865, for about two and a half months, an average of two people a day.
In 1867, they tried to extinguish Campo Maior as the county seat, adding Ouguela to it and attaching it to the municipality of Elvas. Such a decision causes a collective uprising of the village, which on December 13, enters a real general strike.
The municipality is definitely added to its only rural parish, in 1926 – Nossa Senhora dos Degolados.