What Was the Most Important Battle of the Hundred Years' War?
The question is unanswerable in the abstract, but the answer is not. The most important battle of the Hundred Years’ War was Castillon, fought on 17 July 1453 on the banks of the Dordogne, because Castillon was the battle that ended the war. Bordeaux surrendered on 19 October 1453, the English were left with Calais alone, and the dynastic question that had opened the war in 1337 was finally settled in favour of the Valois. The argument can be made for other candidates — Crécy, Poitiers, Agincourt, the relief of Orléans — and the strongest of the alternatives is Agincourt. But the battle that ended a 116-year conflict is, by definition, the one that decided it.
The argument for Castillon is therefore the argument that the war was decided in 1453, not in 1346 or 1356 or 1415 or 1429. The earlier battles were decisive within their phases: Crécy established the tactical dominance of the English longbow, Poitiers gave the English the territorial settlement of Brétigny, Agincourt gave Henry V the legal settlement of Troyes. None of them ended the war. Each was followed by a French recovery that undid the English gains. The French recovery of 1429–1453, by contrast, was not followed by an English recovery, because by 1453 the English had run out of money, of men, and of political will.
The case for Castillon
The Battle of Castillon was the last battle of the war, and it decided the war. The French position, fortified and defended by a substantial train of field artillery under Jean Bureau, was attacked on 17 July 1453 by John Talbot, Earl of Shrewsbury, in his late sixties and one of the last of the great English captains. Talbot attacked without proper reconnaissance, his army was caught in the open by the French cannon, and the English force was destroyed in detail. Talbot and his son John Talbot, Viscount Lisle, were killed. The English position in Gascony collapsed; Bordeaux, the principal English possession in the south, surrendered on 19 October 1453.
Castillon is conventionally cited as the moment when the gun replaced the longbow as the dominant battlefield arm. The argument is not exactly right — the longbow and the field gun had been in use simultaneously for a century, and the longbow was still a formidable weapon in 1453 — but the direction of the argument is. The French train of field artillery, built by the Bureau brothers, was the most powerful in Europe by 1450, and Castillon was the moment at which its decisive effect was demonstrated. The longbow had not been defeated in detail; it had been outclassed by a different kind of weapon, used in a different way.
The political consequences of Castillon were immediate. The English, having lost their continental possessions, were now an island kingdom. The Plantagenet dynasty had been a continental dynasty; it was now an English dynasty, and the political crisis of the 1450s — the loss of Normandy in 1449, of Gascony in 1451, the war in 1453, the mental breakdown of Henry VI — fed directly into the Wars of the Roses. The argument of Édouard Perroy, in La Guerre de Cent Ans (1945), that the loss of France was the necessary precondition of the modern English state, is the standard modern treatment.
The case for Agincourt
The strongest case for a different answer is the case for Agincourt. The Battle of Agincourt, fought on 25 October 1415, was the most concentrated English victory of the entire war: an English army of perhaps 6,000 destroyed a French force of perhaps 12,000–18,000, killed a substantial proportion of the higher French nobility (the Duke of Alençon, the Duke of Brabant, the Constable d’Albret, the Count of Nevers), and lost perhaps 400–600 of their own number. The English were outnumbered by between two and four to one. The engagement has been celebrated, by Shakespeare and by the long historiographical tradition, as the moment when English arms reached their highest pitch of perfection.
The political consequences of Agincourt were substantial. The conquest of Normandy (1417–1419), the Treaty of Troyes (1420), and the apparent settlement of the dynastic question in favour of the Lancastrian line were the long-term consequences of the day. The battle is, in the sense that matters to English memory, the most important battle of the war. It is not, however, the most important battle of the war in the sense that decided the war, because the war continued for 38 more years after Agincourt and was eventually lost.
The case for the relief of Orléans
The case for the relief of Orléans is the case for the turning point. The English position in France, which had looked nearly impregnable in 1428, collapsed after the arrival of Joan of Arc at Orléans on 29 April 1429, the lifting of the siege on 8 May, the victories of the Loire campaign in June, and the coronation of Charles VII at Reims on 17 July 1429. The English lost Normandy in 1449, Gascony in 1451, and the war in 1453. The argument of the 19th-century French historians — and of the modern French school from Contamine to Curry — is that the relief of Orléans was the moment at which the war changed sides.
The argument has force, but the relief of Orléans was not, in the strict sense, a battle. It was a campaign, and the most decisive engagement of the campaign was Patay, on 18 June 1429. The English army of Lord Talbot was destroyed in a single day, and the French cavalry advance, not the longbow, was the decisive factor. The battle that decided the campaign of the Loire was, in this sense, Patay, and the campaign of the Loire was the political and military foundation of the French reconquest.
The case for Crécy and Poitiers
The case for Crécy and Poitiers is the case for the tactical founding moment. The Battle of Crécy, on 26 August 1346, was the first great demonstration of the longbow in the field, and it set the tactical template that the English would use, with variations, for the rest of the war. The Battle of Poitiers, on 19 September 1356, was the tactical refinement of the Crécy template, and the capture of King John II of France at Poitiers was the basis of the Treaty of Brétigny. The two battles are the foundation of the English tactical system, and they are the battles that have been most studied by military historians.
The case for Crécy and Poitiers, however, is the case for the English tactical system, not for the most important battle of the war. The English tactical system was defeated in the 15th century, not by the longbow being beaten in detail but by the French development of new tactical systems (dismounted men-at-arms, crossbowmen with pavises, field artillery) that the longbow could not counter. The argument of Philippe Contamine, in La Guerre de Cent Ans (1968), is that the war was decided by tactical innovation, not by tactical tradition, and that the decisive innovation was the French field artillery.
The verdict
The most important battle of the Hundred Years’ War was Castillon, because Castillon ended the war. The most spectacular English victory was Agincourt, and the tactical founding moment of the English tactical system was Crécy. The case for Orléans is the case for the political turning point, and the case for Poitiers is the case for the most consequential single capture. Each of these answers is defensible; each identifies a different kind of importance. The question itself is a measure of the war’s complexity.