If you spend enough time reading fourteenth-century chronicles, you start to realize that medieval chroniclers were rarely interested in women unless those women were either saints or catastrophes. Men like Jean Froissart or Jean le Bel wrote for an aristocratic audience that wanted tales of chivalric prowess, lance-strokes, and the grand legal chess match of dynastic succession. So when both le Bel and Froissart suddenly pause their sweeping narratives of the Hundred Years’ War to marvel at a countess in full mail riding a warhorse through the streets of a burning Breton town, you have to sit up and pay attention. Something extraordinary happened at Hennebont in the spring of 1342.
 

Yet separating the real Joanna of Flanders—known to Breton memory as Jeanne la Flamme ("Fiery Joanna")—from the romanticized legend requires looking past the nineteenth-century paintings and digging into the brutal, claustrophobic reality of fourteenth-century siege warfare and feudal law. When you look at the primary sources side by side, what emerges isn't a fairy tale of a damsel playing at knighthood. It is a ruthless, high-stakes struggle for political survival fought by a woman who understood military logistics and human psychology better than the seasoned captains sitting on her war council.

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The Legal Knot: Why Brittany Caught Fire

To understand why Joanna found herself trapped behind the granite walls of Hennebont in May 1342, we first have to untangle the mess that Duke John III of Brittany left behind when he died childless in April 1341.
 

People often imagine feudal inheritance as a clean, rigid set of rules—primogeniture, eldest son takes all, case closed. In practice, medieval property law was a patchwork of contradictory local customs, and when a great fief had no direct male heir, the law became whatever you had the swords to enforce. In Brittany, the succession came down to two claimants:
 

1. Charles of Blois, who claimed the duchy through his wife, Joan of Penthièvre (the niece of the late duke, via a deceased younger brother).

2. John of Montfort, the late duke's half-brother, who argued that as a closer male blood relative, his claim superseded that of a niece.
    

If this had happened fifty years earlier, it might have remained a bitter regional squabble. Instead, it exploded right in the opening decade of the Hundred Years’ War. Charles of Blois happened to be the nephew of King Philip VI of France. Naturally, the French legal court at Conflans ruled in favor of Charles in September 1341. That left John of Montfort with only one play: he turned to King Edward III of England, who was claiming the French throne himself. Overnight, Brittany became the proxy battleground for the two superpowers of Western Europe.
 

Then, everything went wrong for the Montfortist cause. Late in 1341, French forces cornered John of Montfort at Nantes. Whether through treachery or sheer exhaustion, Nantes capitulated, and Montfort was hauled off to the Louvre in Paris as a prisoner.  By every conventional metric of medieval politics, the War of the Breton Succession should have ended right there. In fourteenth-century warfare, capturing the rival claimant was checkmate; a faction without a lord was a body without a head. Charles of Blois and his French backers certainly assumed the war was over, expecting only a spring campaign to mop up the remaining Montfortist garrisons. They simply failed to account for Montfort’s wife.
 

From Rennes to the Blavet: A Calculated Retreat:

Joanna of Flanders was around forty-six years old when her husband was captured—a crucial detail that often gets lost. She was not an impulsive twenty-year-old bride; she was a seasoned noblewoman shaped by one of the most politically volatile families in Europe. As the daughter of Louis I, Count of Nevers, and sister to the Count of Flanders, she had grown up watching Flemish cities, French kings, and English merchants tear at one another for decades.
 

When word reached Joanna at Rennes that her husband was in a French dungeon, she didn't retreat to a convent or sue for terms. According to Froissart—who drew heavily here from the earlier chronicle of Jean le Bel—she immediately walked into the hall holding her young son (also named John), showed the boy to her demoralized knights, and declared that the loss of one man could not ruin their cause when his heir stood right before them.
 

Now, historians always have to read speeches in medieval chronicles with a healthy dose of skepticism; chroniclers loved inventing stirring rhetoric in the tradition of classical Roman historians. However, we don't need to take Froissart's exact words as a verbatim transcript to see what Joanna actually did. Her actions are documented across multiple administrative and narrative records. She emptied her treasuries at Rennes and Brest to pay mercenaries on the spot, reorganized her garrisons, dispatched her close advisor Amaury de Clisson across the Channel to broker an urgent military alliance with Edward III (which included securing safe passage for her young children to England), and moved her headquarters to Hennebont.
 

Why Hennebont? Look at a map of southern Brittany and the brilliance of her choice becomes obvious. Rennes was inland; if Charles of Blois surrounded her there, English ships could never reach her. Hennebont, by contrast, sat at the head of the tidal estuary of the River Blavet. It had formidable stone walls, a towering castle keep, and direct maritime access to the Atlantic. As long as the river channel stayed open, England could feed her troops and land reinforcements. Joanna wasn't hiding; she was holding the lock to the front door of Brittany.
 

Blood, Smoke, and the Raid on the French Camp:

In May 1342, Charles of Blois arrived outside Hennebont with a massive Franco-Breton army, led on the field by hardened commanders like Louis of Spain and Hervé de Léon. They had just battered the nearby city of Rennes into submission and expected Hennebont to fold quickly.
 

The fighting began the moment the vanguard arrived. Rather than waiting passively behind the ramparts, the garrison sortied out to clash with the attackers at the palisades. When the assault intensified in the days that followed, Joanna placed herself directly in the line of sight. She put on armor, mounted a courser, and rode from street to street, rallying the men-at-arms and ordering the women of Hennebont—nobles and townsfolk alike—to tear up the cobblestone streets, carry the stones up to the battlements, and haul up pots of quicklime to hurl down on the attackers scaling the walls.
 

If you have never worked with unslaked lime, it is worth pausing to appreciate how terrifying a weapon it was. Quicklime reacts violently with moisture—meaning sweat, eyes, or open wounds—causing blinding chemical burns inside the visor of a bascinet helmet.
 

Then came the moment that cemented Joanna’s reputation across Europe. During a ferocious all-day assault, Joanna climbed one of the high towers to survey the battlefield. Looking past the frontline trenches, she noticedsomething the men fighting on the walls could not see: almost the entire French army had moved forward to watch or participate in the assault, leaving their sprawling tent camp in the rear virtually unguarded.
 

What happened next reads like madness on paper, yet it was cold tactical calculation. Joanna came down from the tower, mounted her horse, gathered around three hundred horsemen, and rode quietly out of a postern gate on the side of the town opposite the fighting. Circling unseen behind the Franco-Breton lines, she led her riders straight into the enemy camp, cutting down the skeleton crew of guards and setting fire to the pavilion tents and supply wagons.
 

Within minutes, a massive column of black smoke rose behind the French army. In medieval warfare, fire in your own baggage train meant one of two things: either a relief army had arrived to take you in the rear, or your entire supply of food, horses, and armor was turning to ash. Panic rippled through the attackers. Louis of Spain abandoned the assault on the walls and wheeled his forces around to save the camp.
 

Seeing the entire French army suddenly turning on her three hundred riders, Joanna knew she could not cut her way back through the main gate of Hennebont. Instead, she spurred her horse along the road toward the nearby stronghold of Auray (Brest, in some lesser accounts), drawing a furious French cavalry pursuit away from the battered town.
 

For five days, the defenders of Hennebont had no idea if their countess was dead or captured. Then, under cover of darkness—having rallied fresh riders at Auray—Joanna slipped right back through the French siege lines with banners flying and trumpets sounding at the gate, riding back into Hennebont to the deafening cheers of the garrison before the enemy could intercept her.
 

The Psychological Breaking Point and the Sails on the Horizon:

This is the point in the story where historians have to confront a major debate over our sources. For decades, nineteenth- and early-twentieth-century military historians—many of whom were deeply uncomfortable with the idea of a woman exercising direct battlefield command—tried to argue that Froissart exaggerated Joanna’s role for chivalric drama, suggesting that her captain, Sir Yves de Tréziguidy, must have been the real mastermind.
 

Modern medievalists largely reject that dismissal, and for good reason. First, Froissart didn't invent the story; he lifted the core narrative from Jean le Bel, a sober, contemporary Flemish chronicler who had direct contacts among the English and Hainault knights who fought in Brittany in 1342. Second, the French and Breton chronicles sympathetic to Charles of Blois—writers who had every reason to belittle Joanna—never deny her command at Hennebont. In fact, we know that many noblewomen in the fourteenth century defended castles when their husbands were absent (Philippa of Hainault, Agnes Dunbar at Dunbar Castle, and later Jeanne de Clisson all operated in this sphere). Where historians do debate is the exact chronology of the siege's final days and how close Hennebont actually came to treachery.
 

After Joanna’s return, Charles of Blois realized he could not take the town by storm without unacceptable losses. He divided his army: taking part of his host to besiege Auray, he left Louis of Spain and Hervé de Léon outside Hennebont with twelve massive siege engines—trebuchets brought up from Rennes—to pound the town into rubble day and night.
 

Here, the physical horror of a fourteenth-century siege set in. The constant concussion of hurled boulders shattered rooftops and cracked the curtain walls. Sleep became impossible. Food ran low. Worse still, Hervé de Léon had a psychological weapon right inside the castle: his own uncle, Guy de Léon, the Bishop of Léon, was inside Hennebont nominally serving on Joanna’s council.  Meeting secretly outside the walls under a flag of truce, Hervé convinced his uncle the bishop that the English were never coming, and offered complete amnesty to the garrison if they surrendered the town—and Joanna—to Louis of Spain. The bishop went back inside and began working on the exhausted Breton lords. By late June, the walls were so badly breached that the lords were ready to yield. Joanna begged them on her knees to wait just three more days, convinced that the English wind would turn. The bishop and the council ignored her tears and scheduled a meeting at the gates for the following morning to formally hand over the keys.
 

How close was that betrayal? Chroniclers tell us that on the very morning the bishop walked toward the gate to finalize the surrender, Joanna—looking out toward the sea from a high window in despair—spotted the dark specks of sails rounding the bend of the Blavet estuary.
 

"I see the succors I have so long wished for!" she cried out from the casement.
 

It was Sir Walter Mauny, an aggressive veteran commander of Edward III’s household, arriving with a fleet that had been delayed for weeks by fierce headwinds in the Channel. Carrying a force of elite English longbowmen and men-at-arms, Mauny sailed right into the harbor. The Bishop of Léon hastily abandoned the surrender talks, slipped out of town to join the French camp, and the revitalized defenders—now backed by English archers—marched out to smash the great siege engines that had terrorized them for weeks. Realizing that a town resupplied from the sea with English longbowmen on the walls was impregnable, Louis of Spain broke camp and retreated.
 

The Tragic Epilogue History Rarely Mentions:

If the Siege of Hennebont were a piece of fiction, the story would end on the battlements with the French marching away in defeat and Walter Mauny kissing the Countess’s hand. And in a military sense, Joanna’s stand at Hennebont completely altered the course of the War of the Breton Succession. By holding the port until the English arrived, she prevented a quick French victory, kept the Montfortist claim alive for twenty-two more years, and ensured that in 1364, the son she had held up in the hall at Rennes would eventually triumph at the Battle of Auray to become Duke John IV of Brittany.
 

Yet the human cost to Joanna herself is one of the darkest, most fiercely debated mysteries of fourteenth-century history.

Shortly after the relief of Hennebont and a subsequent naval clash on her return voyage to England in late 1342, Joanna of Flanders abruptly vanishes from the front lines of historical chronicles. For five centuries, nobody could quite explain why the fiercest commander in Brittany simply stepped off the stage right after her greatest triumph. It wasn't until Victorian historians began combing through the royal exchequer rolls of Edward III in London—the dry, meticulous accounting ledgers of the English crown—that the truth surfaced.
 

From late 1343 until her death in 1374, Joanna of Flanders was kept in honorable confinement at Tickhill Castle in Yorkshire under the care of royal custodians. Even when her husband escaped French captivity in 1345, and even after her son reclaimed the Duchy of Brittany two decades later, Joanna never went home. Why? Here, historians remain sharply divided into two camps:
 

• The Psychological Collapse Thesis: Traditional historians argue that the sheer, unrelenting trauma of 1341–1342—the loss of her husband, the months of starvation and bombardment at Hennebont, the constant threat of betrayal by her own council, and a brutal sea battle on the way to England—triggered a permanent nervous breakdown or severe psychiatric illness, forcing Edward III to place her in quiet care at Tickhill.

• The Political Hostage Thesis: A growing number of revisionist medievalists point out that Edward III was a cold, pragmatic politician. Once English troops were on the ground in Brittany, an independent, fierce-willed countess with close blood ties to the French-aligned House of Flanders was a dangerous wildcard. By declaring her "indisposed" and keeping her and her children under tight English guardianship in Yorkshire, Edward III effectively took direct control of the Breton war effort and its revenues without having to answer to the woman who had saved it.
   

We may never know whether the quiet walls of Tickhill Castle held a woman broken by the horrors of Hennebont, or a political prisoner silenced by her own allies because she was far too formidable to control. What remains beyond dispute is what happened in the smoke and stone of May and June 1342. When the men around her calculated the odds and prepared to open the gates, Joanna of Flanders looked at the same burning town, strapped on her mail, and refused to let history erase her house.

Primary Sources & Chronicles:
 

Froissart, J. (1901–1903). Chronicles of England, France, Spain, and the adjoining countries (G. C. Macaulay, Ed.; T. Johnes, Trans.). Macmillan. (Original work composed 14th cent.)

(Note: Froissart's accounts of Joanna of Flanders and the 1342 siege draw heavily upon the earlier, foundational work of Jean le Bel).

Le Bel, J. (1904–1905). Chronique de Jean le Bel (J. Viard & E. Deprez, Eds.). Société de l'Histoire de France. (Original work composed c. 1352–1363).
 

Modern Historical Studies & Reference Works:
 

Astill, G., & Grant, A. (Eds.). (1988). The countryside of medieval England: A sourcebook of material evidence. Blackwell.

Contamine, P. (1984). War in the Middle Ages (M. Jones, Trans.). Basil Blackwell.

Curry, A. (2003). The Hundred Years' War (2nd ed.). Palgrave Macmillan.

Jones, M. (1988). Creation of Brittany: A late medieval state. Hambledon Press.

Jones, M. (1991). Ducal Brittany, 1364–1399: The relations of policy and politics in the duchy of an independent lord. Oxford University Press.

Jones, M. (Ed.). (1982). The register of Edward the Black Prince preserved in the Public Record Office. H.M. Stationery Office.

(Contains financial and administrative records from the English Exchequer regarding the management of the Breton campaign and the maintenance of royal wards).

Sumption, J. (1990). The Hundred Years' War: Trial by battle (Vol. 1). University of Pennsylvania Press.