[Joan of Constantinople, 1849, Félix de Vigne, Album du cortége des Comtes de Flandre, source: Wikimedia Commons]
Jeanne was the daughter of Baldwin IX of Flanders and Marie of Champagne, who was the granddaughter of Eleanor of Aquitaine and Louis VII of France. Baldwin left on the Fourth Crusade in 1202. Marie joined him two years later when he was crowned Latin Emperor of Constantinople, leaving Jeanne and her sister Margaret under the guardianship first of their uncle and regent Philip of Namur,* then the French king Phillip II. The girls were raised at the French court where they almost certainly met Blanche of Castile, who would later be a political figure in both of their lives as Queen of France.
[The capture of Ferdinand of Portugal, 14th century, Grandes Chroniques de France, source: Wikimedia Commons]
This left Jeanne as the sole ruler of Flanders and Hainaut. She aimed to build up the power of the towns against the barons, supporting the construction of markets, government buildings, and canals and reducing taxes on certain members of the wool trade. She also lent her support to two religious groups: Cistercian nuns and the beguines. In 1225 she faced a challenge to her position. A man claiming to be her father tried to stir up trouble and win control of her lands. He was exposed as a fraud not long after and imprisoned.
Ferdinand was finally released in 1226 at the instigation of Blanche of Castile and joined his wife’s governance. Jeanne ruled alone again for four years before marrying Thomas II of Savoy, partially at Blanche's urging. She died in 1244, leaving Flanders and Hainaut to her sister Margaret.
*Baldwin’s younger brother
**Louis claimed it belonged to him, as it had been part of Isabelle of Hainaut’s dowry and he was her son. Jeanne may or may not have been as much involved in the concession as Ferdinand, but the Flemish unilaterally blamed him.
***Her half-great-uncle. He was her mother’s mother’s half-brother.
Joan of Constantinople, Countess of Flanders - Epistolae
Simons, Walter. Cities of Ladies: Beguine Communities in the Medieval Low Countries, 1200-1565. Philadelphia: University of Pennsylvania Press, 2003.
Nichols, John A. and Lillian Thomas Shank, eds., Distant Echoes: Medieval Religious Women, Volume One. Kalamazoo, MI: Cistercian Publications, 1984.
Joan, Countess of Flanders - Wikipedia