It was signed in Layrac, France in October 1252, and said she was intended to marry the count Roger-Bernard III of Foix,[1] but the marriage didn't take place until fifteen years later, in 1267.

Then, in a show of dominance, Roger-Bernard changed the family's coat of arms to be a combination of designs from both Foix and Béarn.

In 1293, after three years of peace, Margaret's brother-in-law (Mathe's husband) Gerard VI finally contested the property of Béarn and began a long war with Roger-Bernard over the rights of the sisters who were their wives.

[5] The principality at times was expanded to include Andorra and parts of Basque Country, now located in northern Spain and southern France.

Because Béarn was an independent state, it was the subject of attempted takeovers over the centuries until it was annexed by France in 1620 when King Louis XIII marched into the area with a large army, seized the nobles' estates and, sitting on his new Béarnese throne, declared that the lands were now part of France, thereby ending the principality's sovereignty.