Siege of Novi Zrin ( 1664 ) The Siege of Novi Zrin ( ; ; ; ) in June / July 1664 was last of the military conflicts between the Croatian forces ( with allies ) led by Nikola Zrinski , Ban ( viceroy ) of Croatia , and the Ottoman army commanded by Köprülü Fazıl Ahmed Pasha , Grand Vizier , dealing with possession of Novi Zrin Castle , defended by Croats , situated on the bank and marshy islands of Mura River , that formed a border line between Međimurje County in northern Croatia and southwestern part of Hungary , at the time occupied by the Ottomans . The battle resulted in destruction of the castle , and retreat of the Croatian crew , that was forced to withdraw to safer territory of inland Croatia . Historical background . Despite local skirmishes and battles along the Ottoman border with Croatia , Hungary and Transylvania at the beginning of the 1660s , there was a period of unstable and insecure ( " tacit assumption " ) temporary peace between the Habsburg Monarchy and the Ottoman Empire . It seemed that both sides wanted to keep it ; however , Leopold I of Habsburg , twenty - year - old inexperienced Emperor , under strong influence of his advisors , feared Ottoman campaign towards Vienna and possible siege of the Austrian capital , so he kept the majority of his military forces close to Vienna . At the same time , Nikola Zrinski , brave and skillful warrior , well - known all over Europe , demanded support from Viennese court to consolidate and reinforce the border line in northern Croatia through new fortification s that would parry and neutralize the Ottoman threat from Kanije Eyalet in the occupied southwestern Hungary , but with no success . In 1661 Zrinski started to build a new stronghold , Novi Zrin Castle , on his own , at confluence of the Mura River with the Drava , finishing it during 1662 . Since then the castle was attacked several times by the Ottomans , especially in 1663 , but the defence was solid and successful . Siege . At the beginning of June 1664 a large Ottoman army , numbering up to 100 , 000 men ( some sources mention even much more ) , including around 40 , 000 Ottoman and 30 , 000 Tatar fighters , led personally by the Grand Vizier Köprülü , was moving from Constantinople to the northwest and approaching Novi Zrin ( later to fight in the Battle of Saint Gotthard on 1 August 1664 ) . The defenders of Novi Zrin consisted mostly of Croatian and German soldiers ( around 3 , 000 men in total ) , while the majority of the Habsburg army ( 30 , 000 men ) , situated in the camp near Saint Gotthard , was waiting for the result of the battle . On 5 June 1664 Köprülü ordered siege and continuous attacks upon the castle . After a few weeks of fighting , with exhausted defenders receiving only insignificant reinforcements from the Emperor ' s headquarters , the Turks managed to dig " lagums " - underground tunnels - below the bastion s and ignited gunpowder to blow them up . On 7 July 1664 the strong explosions destroyed some parts of the walls making big holes . Aggressors consequently rushed and penetrated into the castle . The surviving and enormously outnumbered Croatian defenders were forced to withdraw from the castle and to abandon the Mura River area . Ottoman commanders gave the order to their soldiers to ruin Novi Zrin completely to the ground and then moved further with the whole army to the north , first to Kanije and then towards Saint Gotthard . Aftermath . The destruction of Novi Zrin , together with a little bit later ( on 10 August 1664 ) signed " unfavourable and shameful " Peace of Vasvár , made Nikola Zrinski and other leading Croatian and Hungarian magnates angry and initiated the Zrinski - Frankopan conspiracy . Later in the same year Zrinski died , allegedly killed by the wild boar , but the rest of magnates continued the conspiracy , which ended tragically in 1671 . Novi Zrin was never rebuilt . Today there is only a memorial obelisk on the place where the castle once was .