The siege of La Rochelle (December 1572-July 1573) was the main military action of the Fourth War of Religion, and was an unsuccessful Catholic attempt to capture the main Huguenot stronghold.
In the aftermath of the St Bartholomew's Eve Massacre (24 August 1572) a stream of refugees arrived in La Rochelle, one of the main Huguenot strongholds during the earlier wars of religion. Within a few weeks the city was defended by a garrison of around 1,500 men, but it was already threatened by a Royal force being raised at Brouage, twenty five miles to the south. This force included an army and a fleet, and had originally been raised to take part in a possible expedition against Spain.
Charles IX was aware of the danger of a long siege, and so soon after the massacre sent messages to La Rochelle assuring the citizens that he intended to respect their religious rights. Marshal Biron, one of the more moderate Catholics, was appointed as the new governor of La Rochelle.
The citizens of La Rochelle did not believe Charles's assurances, and Biron was refused entry to the town. Charles was still unwilling to risk a siege, and the city was not even blockaded until December. At the same time the king convinced the Protestant leader François de la Noue to attempt to convince the townspeople to accept his terms.
On 4 December Biron finally appeared outside La Rochelle at the head of his army and began the blockade of the city. By this point La Rochelle was defended by around 1,200 regular troops and 2,000 volunteers, while Biron commanded a much larger force.
The siege became rather more serious in mid-February 1573 after the arrival of Henry of Anjou (the future Henry III) at the head of a large Royal army which contained five dukes and three marshals as well as a strong artillery force.
The last hope for a negotiated end to the standoff ended on 12 March when La Noue left the city. Ten days later, on 22 March, the first artillery bombardment began. Anjou's army was strong in artillery, with 42 cannon and great culverins, supported by 354 men from the Paris Arsenal. During the course of the siege these guns would fire 35,000 cannon shot, starting with 1,500 on 22 March.
The first of eight major and twenty-one minor assaults was made on 7 April. By now the bombardment had breached the walls, but this attack stalled at the foot of the bastion de l'Evangile. Anjou was unable to renew the assault on 8 April because he had only had 100 cannon balls left, but more assaults were launched on 10, 13 and 14 April. On the last of those days a mine was detonated bringing part of the Bastion down on some of Anjou's men, and another five assaults failed. Major assaults also failed on 30 May and on 11 June, when some of the attackers reached the ramparts before being repulsed.
By this point the Royal army had suffered heavy casualties, amounting for half of the army - out of 40,000 men 10,000 had been lost in combat and 12,000 from disease. Inside the city the defenders had suffered a smaller ratio of losses - 1,300 out of 3,100.
The court was finally offered a way out of the siege when Henry of Anjou was elected King of Poland. This gave Charles IX an excuse to begin negotiations with the defenders of La Rochelle, and by the end of June the terms of the peace had been agreed. The Huguenots were given the right to free Public worship in La Rochelle, Montauban and Nismes, but lost the wider rights they had gained at the end of the first three wars of religion. This treaty was unacceptable to the defenders of Sancerre, who held out until they were granted the same terms in August.