Siege of ' s - Hertogenbosch The Siege of ' s - Hertogenbosch was in 1629 an action of the Eighty Years ' War in which a Dutch Republican army captured the city of ' s - Hertogenbosch which had been loyal to the King of Spain since 1579 and thus part of the Spanish Netherlands . Background . The Twelve Years ' Truce ended in 1621 . Stadtholder Maurice of Orange had in the meantime played a part in instigating the Thirty Years ' War in Germany . The Habsburgs tried to punish the rebellious Dutch Republic by cutting it off from its " hinterland " by a land blockade . ' s - Hertogenbosch was the main fortress in this perimeter and enormous sums of money were poured into the improvement of its defences . As the ground surrounding the city was a marsh , the city was generally deemed to be impregnable , as the water - saturated soil seemed to make an application of current siege methods impossible ; trench - digging and undermining were apparently out of the question . Maurice had failed twice in taking the city . The blockade caused an economic crisis for the Republic and it reacted by trying to harm the enemy in its colonies . In 1628 one of the many schemes undertaken met with spectacular success when Admiral Piet Hein of the Dutch West India Company captured the Spanish treasure fleet . The vastly improved financial situation of the Republic allowed for a major counter - stroke and Stadtholder Frederick Henry decided to break the Habsburg morale by conquering their main stronghold in the Netherlands . This came very unexpectedly ; most had predicted the goal of his campaign would be Breda , retaken by the Habsburgs in 1625 . Siege attack . Advancing from Grave he laid siege to the city in April 1629 , with an army of 24 , 000 infantry and 4 , 000 cavalry . He also had hired 4 , 000 peasants and these would cause a tactical surprise . Frederick Henry diverted the two main streams feeding the swamps ( the Dommel and the Aa ) around the city by means of a double forty kilometre dike , in the form of a giant square , completely enclosing the fortress . Thus having created a polder , he began to drain it with ( mainly horse ) mills . After the soil had sufficiently dried out his trenches could approach the city walls . Noble visitors from all over Europe visited the siege to admire the novel and spectacular method . Reaction from Habsburg . Of course the Habsburg authorities didn ' t remain idle while their main bulwark was being reduced . They sent a large relief army under command of Frederick Henry ' s Catholic cousin Hendrik van den Bergh , reaching the city in July . Van den Bergh quickly found out that his cousin ' s circumvallation , successfully tested at the siege of Grol in 1627 , was too strong to breach . He tried to lure Frederick Henry away by invading the Republic through the Veluwe , capturing Amersfoort on 14 August . When his supply base at Wesel was taken , he had to withdraw . Meanwhile the Protestant forces dug themselves ever closer to the city along the southern road from the direction of Vught , continuously bombarding the defences . During the siege 28 , 517 cannonballs were fired . On 18 July the large Fortress Isabella fell , followed the next day by Fort Anthony . Despite repeated sallies by the 2 , 500 men of the garrison , the attackers slowly worked their way to the southern city gate . There they undermined Bastion Vught ; in the early hours of 11 September a massive explosion caused a large breach in the ramparts . On 14 September its military governor Anthonie Schetz surrendered the city . Negotiations . Bishop Michael Ophovius tried to plead with Frederick Henry for religious tolerance , but though the stadtholder himself would gladly have granted religious freedom to the Catholics , as he tried to gain popularity in the Spanish Netherlands in the hope support for the rebellion would grow , due to vehement Calvinist resistance it had already been decided to be as strict in this respect as in the rest of the Republic ; only nunneries could remain until the last nun of those present in 1629 had died . Fall of Den Bosch . The fall of ' s - Hertogenbosch was an enormous blow to Habsburg prestige . Their position in the North would soon crumble and Frederick Henry , encouraged by the success , would start a series of other sieges , assisted by his cousin Van den Bergh , who changed sides after being accused of treason . Although its population would remain predominantly Catholic , ' s - Hertogenbosch would stay firmly in the hands of the Republic as part of the Generality Lands until French revolutionary forces captured it in 1794 ; only then would the Batavian Republic grant equality to Catholics . The former Duchy of Brabant remains divided to this day between Belgium ( Brabant ) and the Netherlands ( North Brabant ) .