The battle of St Quentin (10 August 1557) saw the Spanish defeat a French army that was attempting to get reinforcements to the besieged garrison of St Quentin (Fifth Hapsburg-Valois War).
In February 1556 Henry II of France and the Emperor Charles V had agreed the Truce of Vaucelles, which was meant to last for five years. Almost inevitably the peace didn’t last that long. Pope Paul IV managed to engineer an incident in Italy that triggered his defensive alliance with France. In response Henry II send his main army, under Francis, duke of Guise, across the Alps to aid the Pope. This ended the Truce.
Philip II responded by gathering a large army of around 45,000 men, under the command of Emmanuel Philibert, duke of Savoy. This army invaded Picardy, and on 2 August arrived outside St Quentin. On the next morning Admiral Coligny arrived with 800 reinforcements, and took command of the defence. The siege of St Quentin would eventually last for a month, and badly disrupted Philip's plans.
While Coligny was trapped in St Quentin, Anne de Montmorency, Constable of France, attempted to raise a relief army. He eventually managed to gather around 26,000 men - not enough to risk a battle, but enough to attempt to try and reinforce Coligny. Montmorency's men arrived near St Quentin on 7 August and were seen from the town.
On 10 August Montmorency decided to try and attempt to get reinforcements and supplies into the beleaguered town. His plan was to cross the river to the west of St. Quentin and get the supplies in via the marsh that protected that part of the town. The forces to cross the river were to be commanded by Colginy's brother François de Andelot.
The operation was bungled from the start. His army advanced to the Somme, but the boats were at the rear of the column, and it took several hours to get them to the river and then to load them. They were then found to be overloaded, and stuck in the mud. The boats were eventually lightened and Andelot did manage to get 500 men into the besieged town.
The Spanish had been caught by surprise by Montmorency's move, but the delays at the river gave them plenty of time to respond. The Spanish infantry crossed the Somme below the town while an cavalry force, led by the Netherlanders Lamoral, Count of Egmont and Philip de Montmorency, Count of Horn, crossed above the town.
Anne of Montmorency now realised that his plan had failed and ordered a retreat, but he was too late. Two leagues from the town his force was intercepted by Philip's men and his army was destroyed. Caught while attempting to retreat they lost 3,000 dead and 7,000 prisoners. Amongst the captives were Montmorency himself, Louis de Bourbon, duke of Montpensier, Leonor d'Orléans, Duke of Longuevill, the count of La Rochefoucauld, Honorat de Savoie, Count of Villars and John Philip, Count of Salm, the Rhinegrave.
News of the defeat reached the garrison on 13 August, but Coligny managed to hold out for another two weeks. The town eventually fell to a Spanish assault on 27 August, in which both Coligny and his brother were captured. By that point Philip was losing interest in the campaign, and in September, much to Savoy's annoyance, he ordered his army to retire back to the Netherlands. Although the battle of St Quentin had been a disaster, Coligny's defence of the town played a major part in preventing Philip from inflicting a really heavy defeat on the French.