The siege of Amiens (April-25 September 1597) was the last major campaign of the Ninth War of Religion, and saw Henry IV recapture the city after it had fallen to a Spanish ruse earlier in the year.
Earlier in the wars Amiens had sided with the Catholic League against Henry, but like many cities changed sides on terms. One of the conditions was that Henry wouldn’t post a royal garrison in the city, but it was still close to the front line, and so Henry chose it as one of his arms and supplies depots for his planned campaign of 1597.
The Spanish governor of nearby Dourlens, Hernando Tello Porto Carrero, decided to try and capture the city. On 11 March a small force of Spanish troops disguised as peasants captured one of the city gates, and allowed a larger force into the city, which fell almost without a fight. Henry was dismayed by the news, which reached him at Paris.
Henry responded by putting in place a series of measures to raise fresh funds and ordered the construction of a siege train. Marshal de Biron was sent ahead to the area of Amiens with 3,000 men to prepare for the siege, while Henry left Paris on 12 March to visit the garrisons in Picardy to make sure they were secure. By the end of March Biron had reached Longpré, just to the west of Amiens on the north bank of the Somme, while other French troops were at Corbie, east of Amiens on the north bank and at Pecquigny, west of Amiens on the south bank. On 5 April Henry designed the siege works, which would to be placed around the northern side of Amiens to prevent any further Spanish troops from reaching the city. He then returned to Paris to try and raise more money.
The Spanish were also suffering from a lack of money, after Philip II was forced to declare bankruptcy in the autumn of 1596. Despite these problems the Archduke Albert, Philip’s governor in the Spanish Netherlands, was eventually able to raise a relief army 28,000 strong.
Biron began work on the siege works north of Amiens in April. His army grew slowly, and when Henry arrived at Amiens on 7-8 June Biron still only had 6,000 infantry and a small force of cavalry. However he had been able to almost complete the lines of circumvallation north of Amiens, the direction from which any relief army would probably have to come. Soon after Henry arrived his army expanded to 12,000 infantry and 3,000 cavalry. At its largest, Henry’s army was 30,000 strong. He had 45 siege guns in his lines, commanded with great skill by François d’Espinay de Saint-Luc, until he was killed by a musket shot on 5 or 8 September.
The defenders of Amiens weren’t entirely passive. On 17 July they launched a sortie which caused significant damage in the siege lines before being fought off.
The Archduke Albert left Douai early in September with 18,000 infantry and 3,000 cavalry, giving him 21,000 men, more than Henry had in his lines at the time. Albert moved south-west from Douai, heading for Amiens. A plan to cross the Somme above Amiens, around Corbie, was rejected as being too dangerous, and instead his army reached the Somme about six miles to the west of the city on 15 September. Albert then split his force, leading the bulk of the army east towards Amiens along the north bank, while a smaller force was sent to try and cross the river.
The wisdom of Henry’s policy of employing his former enemies was now demonstrated. The King himself was away hunting when the Archduke attacked, and the siege force was commanded by Marshal Biron and the duke of Mayenne, until recently Henry’s chief opponent (although Henry returned to the army during the fighting). Mayenne had suggested that Henry should fortify a position at Longpré. As the Spanish approached the fortifications, Mayenne sent reinforcements to the area, and a Spanish attack on the French lines was repulsed. The attempt to cross to the south bank also failed.
Neither Henry nor the Archduke were willing to risk a major battle outside Amiens. On 16 September the Archduke retreated, leaving the garrison to its own devices. Amiens surrendered on 25 September, and Henry entered the city in triumph.
In the aftermath of the fall of Amiens, Henry was free to turn his attention to Brittany, where the duke of Mercouer was the last major nobleman holding out against him. When the Royal army arrived in Brittany, Mercouer came terms with Henry, effectively ending the wars of religion. On 13 April 1598 Henry issued the Edict of Nantes, which largely confirmed the many earlier edicts in favour of the Huguenots, and formed the basis of a religious settlement that lasted until Henry’s grandson Louis XIV overthrew it over 80 years later. A few weeks later the treaty of Vervins (2 May 1598) finally ended the war with Spain. It took longer to end the conflict with the duke of Savoy, but for most of France 1598 marked the end of the Wars of Religion.