Although estimates on the number of troops vary considerably among modern historians, at Bouvines, a French army commanded by King Philip Augustus routed a larger allied army led by Holy Roman Emperor Otto IV in one of the rare pitched battles of the High Middle Ages and one of the most decisive medieval engagements.

Having lost all credibility as emperor following the battle, Otto IV was deposed by Pope Innocent III, leading to Frederick II's accession to the Imperial throne.

The disaster at Bouvines forever altered the political situation in England, as John was so weakened that his discontented barons forced him to agree to Magna Carta in 1215.

Philip had achieved remarkable success in the expansion of his realm and by the end of his reign, in 1223, had not only laid the foundations for the era of Capetian pre-eminence in Europe which followed and marked much of the Late Middle Ages, but also those of the absolutism that came to define the Ancien Régime.

In 1214, Count Ferdinand of Flanders desired the return of the cities of Aire-sur-la-Lys and Saint-Omer, which he had recently lost to King Philip II of France, in the Treaty of Pont-à-Vendin.

[2] The Emperor finally succeeded in concentrating his forces at Valenciennes, although this did not include John, and in the interval Philip had counter-marched northward and regrouped.

[3] Philip now took the offensive himself, and after manoeuvring to obtain good ground for his cavalry he offered battle on 27 July, on the plain east of Bouvines and the river Marque.

The French army formed up opposite in a similar formation, cavalry on the wings, infantry, including the town militias, in the centre.

[4] It is said by William the Breton, chaplain to Philip at the battle, that the soldiers stood in line in a space of 40,000 steps (15 ha or 37 acres), which leaves very little clearance and predisposes to hand-to-hand fighting.

They provided 3,160 infantry, broken down as: Amiens 250, Arras 1,000, Beauvais 500, Compiegne 200, Corbie 200, Bruyeres 120, Cerny and Crepy-en-Laonnais 80, Crandelain 40, Hesdin 80, Montreuil-sur-Mer 150, Noyon 150, Roye 100, Soissons 160, and Vailly 50.

Châtillon and Melun with their knights broke through the ranks of their Flemish counterparts, then wheeled and struck them from the rear, constantly switching targets.

[16][17] The French urban militia infantry, 2,150 strong, were gathered under the Oriflamme in the centre, in front of Philip's knights and the fleur-de-lis standard.

[20] The battle closed with the celebrated stand of Reginald of Boulogne (Renaud de Dammartin), a former vassal of King Philip, who formed a ring of 400–700 Brabançon pikemen.

[21] Eventually, long after the Imperial army had retreated, the Brabant schiltrom was overrun by a charge of 50 knights and 1,000–2,000 infantry under Thomas de St. Valery.

[4] As well as Reginald of Boulogne two other counts were captured by the French, Hainaut Ferrand and William Longespée, as well as twenty-five barons and over a hundred knights.

[29] Philip returned to Paris triumphant, marching his captive prisoners behind him in a long procession, as his subjects lined the streets to greet the victorious king.

[30] Count Ferdinand remained imprisoned following his defeat, while King John obtained a five-year truce, on very lenient terms given the circumstances.

[31] Longespée was eventually exchanged for a high-ranking French captive, but the Count of Boulogne was imprisoned in a small cell, chained to a log and with little room for movement.

[33] So weakened was the defeated King John that he soon needed to submit to his barons' demands and agree to Magna Carta in 1215, limiting the power of the crown and establishing the basis for common law.

[34] In thanksgiving for the victory, Philip Augustus founded the Abbey of Notre Dame de la Victoire, between Senlis and Mont l'Evêque.

[35] In 1914, to mark the seventh centenary, Félix Dehau had the parish church of Bouvines rebuilt with a number of stained-glass windows representing the history of the battle.