On the 24th October 1415 a force of 6,000 English and Welsh soldiers belonging to Henry V's army catastrophically defeated a French army five times its size. Most of Henry's men were footsoldiers. They faced the massed ranks of France's mounted nobility - heavily-armed knights whose whole lives had been devoted to training for battle, equipped with the best armour, weapons and horses in Europe. By the evening thousands of them would lie in heaps on the battlefield. The English lost 200.

How did Henry's army win a decisive victory against such overwhelming odds? In English mythology, for which we have to thank William Shakespeare and Laurence Olivier, it was due to inspired leadership and better morale. The English also had a technical advantage: the devastating fire of the English and Welsh archers, who could put twelve aimed arrows into the air every minute, gave Henry's army a formidable weapon which the French could not match. But the French knew all about English archery - it had decimated their armies twice before, at Crecy and Poitiers - and their battle-plan hinged on a cavalry charge to annihilate the bowmen right at the outset.

It is still hard to see how the English soldiers, who by St Crispin's Day were a remnant of the host brought over the Channel by 1,600 ships two months before, could have made mincemeat of France's best and bravest. They were wet, cold and hungry. Many were ill, and many more of their comrades had died or been sent back to England as a result of the dysentery which rampaged through their ranks. As far as the English were concerned, their armed incursion into France had proved its point, and now they were on their way home.



They were shocked to discover that the massive French army which had been shadowing them at a distance for several weeks was now arrayed across their line of retreat to Calais. This surprise suggests one reason why the English fought so well: they had to. Whereas the French wanted to teach the English a lesson, and were sure they could, the English had no choice but to crush the French if they were ever to reach home and safety.

For the same reason, the English and Welsh foot-soldiers had no compunction about stabbing the French knights to death as they floundered, dismounted and helpless, in the sea of mud churned up by their horses' hooves. This was not normal conduct in the French practice of battle, which was a pastime for the well-born carried out according to the rules of chivalry. They did not expect to be set upon by grubby commoners with no armour and no shoes. At worst, a noble death at the hands of an equal; failing that, an honourable captivity followed by ransom.

The French plan did not work. The battlefield was not firm and dry. Heavy rain had turned the upland clay into glue; the horses slipped and slithered, encumbered with 200 kilos of rider and armour. What's more, the French didn't stick to their plan. With no single leader the nobles, obsessed by status, squabbled among themselves for the privilege of being the first to cut the English army to shreds.

Imagine five thousand archers shooting heavy, metre-long, armour-piercing shafts into the air at the rate of 60,000 per minute. This hail of death can be compared to the machine-guns which destroyed the British army 500 years later at The Somme. It wrought similar destruction. Men fell and horses panicked, leaving the last pretence of a concerted French attack in tatters.

Henry was a clever general. He had chosen a battlefield which would squeeze the French cavalry between two wooded shoulders as they advanced (as he knew they would). Horsemen need space, and he denied it to them. As the battle progressed, with brave but unco-ordinated attacks by the various French factions, more and more knights fell victim to the archers and went sprawling into the mud, where they were brutally dispatched by the knives of the English foot-soldiers.

Agincourt was not a walk-over. It lasted all day. Henry could not make himself believe that he had won. Even at the very end, there were far more French men-at-arms roaming around the battlefield than English. But as dusk fell, there was no doubt. The field was covered in French bodies - many of them, tragically, fathers and sons - and hundreds of knights had been taken prisoner. The rest had fled. The road to Calais was open.

Was Agincourt a battle lost or a battle won? The French didn't help themselves. Their lack of a unified command-and-control system might have been offset by their sheer weight of numbers, and perhaps that is what they expected... but in fact it proved fatal when faced with the English archery machine, the homicidal approach of the English footsoldiers in hand-to-hand combat, and the do-or-die mentality of the bedraggled English army.

The moral of Agincourt - that a small, well-trained force can beat a far larger army - has echoed through the centuries and has affected English attitudes to their military exploits right up to the Peninsular War. It took Waterloo to show that, if both sides are well-trained, well-armed and well-led, the result is likely to be a 'close-run thing'.