The Mondego Defensive Line used to be a peninsular border separating the kingdoms of Leon and Castile of Cordoba emirate or Taifa’s kingdoms, and, if we consider the division between the Christian and Islamic space, it constituted a European border.
With huge European visibility, fighting for this line was matched in importance only by the pilgrimage to Santa Sé or the crusade to Jerusalem, in a direct relationship between the immediate dangers and spiritual blessings achieved.
From 1085, in response to the Toledo reconquest by Christian troops, the Muslims asked for Almoravids support, a Moroccan dynasty holding particularly zealous Islamic values. They defeated Alfonso VI, at the Battle of Zalaca, in 1086. It was at this time that the Christians resorted to the aid of kingdoms beyond the Pyrenees, of Rome and the Pope. Their appeal brought a large number of francs, knights, second sons of nobility desirous of fame and fortune, but also clerics belonging to religious orders, especially Cluny, to the Iberian Peninsula. The confrontation worsened and became the "holy war".
A vast territory and not a continuous line
The Mondego Defensive Line cannot be interpreted as a continuous and well-defined line. Rather, and especially during the XI century, the boundary was an irregular space where the central powers hardly dominated. While the area of these territories got increased, its domain got smaller, increasing the role of local chiefs, who sometimes acted with great autonomy. As stated by José Mattoso, the "frontier constituted a call for independence." In these extensive and diverse territories, allegiances were precarious. Revolts prevailed and alliances that were the most advantageous at the time.
Spaces of cohabitation, permeability and multiple influences
In this unstable region, diverse cultures coexisting was an inevitable reality and resulted in a social life that was completely independent from political strengths, with solidarity, peaceful relationships, trade and cultural exchanges.
Thus, it is important to define this border as a communion space between two different cultures. This had influences on toponymy and gastronomy, for example.
During de XI century, the area of Coimbra was one of the most prosperous Mozarabic centres (Christian population that was under Islamic domain) with D. Sesnando Davides in power. Born in Tentúgal and taken to the South as a child, Sesnando Davides, was raised in Cordoba and held important positions in Seville. For reasons unknown, he left the Muslim side and served with Christian troops. After the Christian reconquering of Coimbra, in 1064, D. Fernando Magno offered him the regency of the city, and he remained as such until 1091, the year of his death. Sesnando is an unavoidable figure in Mondego Castles and Town Walls, due to his involvement in the construction and advancement of our defensive structures.
Spaces of armed conflict, instability and dangers
Over time the conflict experienced periods intensity and calm, with times of peacefulness and harmony but also with periods of strong militarization and religious intransigence, especially when the Almoravids arrived here in 1086. This was exacerbated by the invasions of Yusuf and Yaqub Almançor and the exhortation of the crusades that the Franks from the north brought with them.
Between these episodes of intransigence, the inhabitants of Soure Castle left after burning it, fearing a defeat to the Muslims.
With the advancement of the border to the Tejo and the subsequent distancing of the war line, the Mondego castles adapted to this new reality: orderly territorial poles headed the administration unifying the population in a strong and consolidated idea of king and kingdom. And of course, continuing to defend the territory against possible invasions from neighbouring kingdoms. Therefore, our defensive structures, during the XIII and XIV centuries, remained in use, and underwent several improvements, especially those situated along the main roads from the borders to the capital.