the historic Béarn, which kept its borders intact until the Revolution. Béarn was included in the original borders given to the Frankish kingdom by the Treaty of Verdun in 843, but the creation of a political entity of their own led to an evolution of this vassalage link. Thus, the gradual accession of Bearn to a de facto sovereignty status is the major theme of this medieval period. From the 11th to the 14th century, Béarn was tossed between the zones of influence of the Dukes of Gascony, the Kings of Aragon, the Kings of England and the Kings of France. Béarn remained under the control of the dukes of Gascony after its division in the 9th century, and this link was already very weak in the second half of the 11th century. Vassalage was only theoretical under Gaston IV the Crusader, who took part in the first crusade and the Reconquista. He played a decisive role alongside Alfonso I of Aragon. Bearn became the ally of Aragon, breaking the last links with Gascony. This alliance was initially balanced, but the union of Aragon with Catalonia in 1137 broke this balance in favour of Aragon. Béarn became a vassal country of the Aragonese crown, which tried to create a vast ensemble on both sides of the Pyrenees. In 1213, the Aragonese defeat at the battle of Muret led to the end of Aragonese interventions in the region. The ties of vassalage between Béarn and Aragon were gradually weakened and then broken, without any clashes, during the first half of the 13th century. This rupture was the occasion for the kings of England to demand the return of Bearn to the Gascon fold. In spite of his desire of independence, Gaston VII pays homage to the king of England in 1240. The return of Béarn to the Gascon sphere of influence is also reflected by a change of capital, Orthez (closer to Gascony) replaces Morlaàs in 1242. Gaston VII will not, in spite of everything, cease to revolt against this intrusion in the affairs of a country which previously had a very broad autonomy. He had to admit defeat after being taken prisoner at Winchester by Edward I of England in 1276. A sovereign principality Gaston VII chose to marry his second daughter, Marguerite de Béarn, to the Count of Foix Roger-Bernard III. This marriage provoked the indissoluble union between the