In pursuit of his claim to the French throne, Henry V of England and an army of about 11,000 men invaded Normandy in August 1415. They took Harfleur in September, but by then half their troops had been lost to disease and battle casualties. Henry decided to move northeast to Calais, whence his diminished forces could return to England. Large French forces under the constable Charles I d'Albret blocked his line of advance to the north, however.
The French force, which totaled 20,000 to 30,000 men, many of them mounted knights in heavy armour, caught the exhausted English army at Agincourt (now Azincourt in Pas-de-Calais département). The French unwisely chose a battlefield with a narrow frontage of only about 1,000 yards of open ground between two woods. In this cramped space, which made large-scale maneuvers almost impossible, the French virtually forfeited the advantage of their overwhelming numbers. At dawn on October 25, the two armies prepared for battle. Three French divisions, the first two dismounted, were drawn up one behind another. Henry had only about 5,000 archers and 900 men-at-arms, whom he arrayed in a dismounted line. The dismounted men-at-arms were arrayed in three central blocks linked by projecting wedges of archers, and additional masses of archers formed forward wings at the left and right ends of the English line.
Henry led his troops forward into bowshot range, where their long-range archery provoked the French into an assault. Several small French cavalry charges broke upon a line of pointed stakes in front of the English archers. Then the main French assault, consisting of heavily armored, dismounted knights, advanced over the sodden ground. At the first clash the English line yielded, only to recover quickly. As more French knights entered the battle, they became so tightly bunched that some of them could barely raise their arms to strike a blow. At this decisive point, Henry ordered his lightly equipped and more mobile English archers to attack with swords and axes. The unencumbered English hacked down thousands of the French, and thousands more were taken prisoner, many of whom were killed on Henry's orders when another French attack seemed imminent.
The battle was a disaster for the French. The constable himself, 12 other members of the highest nobility, some 1,500 knights, and about 4,500 men-at-arms were killed on the French side, while the English lost less than 450 men. The English had been led brilliantly by Henry, but the incoherent tactics of the French had also contributed greatly to their defeat.