Siege of Belgrade ( 1717 ) The siege of Belgrade in 1717 occurred during the Austro - Venetian - Ottoman war , which took place from 1714 to 1718 and after the Austrian victory of Petrovaradin . The siege ended on August 17 , 1717 with the conquest of the stronghold by Austrian troops under the command of Prince Eugene of Savoy . Prologue . After the success of his 1716 campaign , Eugene of Savoy had one main objective : the conquest of the fortress of Belgrade . The city is located exactly at the confluence of the Sava river and the Danube . The fortress , located on an arm of the Sava , can be attacked from the south . The strategic value of this position lies in its walls which can resist both attacks from the south - east and those from the north - west and this makes it a key to the Balkans for both the Austrians and the Ottoman Empire . In 1688 , Belgrade was wrested from the Ottomans after a siege , but two years later , the Ottoman Empire recaptured it . Prince Eugene was seriously wounded during the first siege and now strongly supported the need for a river flotilla on the Danube as being essential for the conquest of Belgrade . The mission of the fleet was to provide assistance and support to the imperial army . Eugene managed to enlist the Emperor ' s support , and the crew for the ships was hastily recruited in the Netherlands . The allies of Austria were Russia , which limited itself to a prudent line of defense , and Poland , both still militarily engaged in the Great Northern War against Sweden and Charles XII . Meanwhile , the states of the Holy Roman Empire provided only a modest cash contribution and Bavaria joined the side of Austria . Preparations . On May 13 , 1717 Prince Eugene left Vienna , with his troops from Futtak . Even before the troops were assembled , on May 21 , Prince Eugene began his march toward Belgrade with about 70 , 000 men , reinforced by 6 , 000 Bavarian and other Austrian troops stationed in the Banat for a total of about 100 , 000 men . In addition , he command the Danube flotilla , consisting of about fifty boats of various types and ten naval vessels armed with light artillery . Eugene wanted to reach the city and begin the siege as soon as possible before any Ottoman troops would reinforce the city . The biggest problem was that the fortress could not be attacked from the south , and progress could only be made after crossing the Danube and the Sava . He chose the direct route , by crossing the Sava river , although , on this side , the defense of the fortress was the strongest . On the advice of one of his generals , he chose to return across the Danube , surprising the Ottomans who did not expect the enemy to cross the river at that point . The Austrian army managed to cross almost intact between June 15 and 16 . Eugene deployed his artillery while the Imperial troops began digging trenches , both in front of the fortress and at the rear of the army . The Ottoman defenders in Belgrade numbered 30 , 000 men . Prince Eugene was informed that an Ottoman army had been sent to relieve Belgrade . This army arrived on July 28 . However , instead of taking action against the besiegers , they also began to dig trenches . Prince Eugene ' s troops were caught between the fortress and the relief army . Because of losses to cannon fire as well as malaria , the strength of the Austrian army was slowly diminishing . The final battle . The situation became perilous because the Ottomans wanted to let the enemy wear themselves down in a long siege . While the situation was rather worrying for the imperial troops , on August 14 , Belgrade was suddenly shaken by a powerful explosion : a mortar shell struck the powder magazine inside the fortress and 3 , 000 defenders were killed in the explosion . At this time , Eugene ordered an attack on the Ottomans for the next day : at midnight , on August 16 , the attack began with infantry in the center and cavalry on the wings . Apart from those men necessary to defend the trenches facing the fortress , the entire army was involved in the attack . The night attack surprised the Ottomans ; after the first hours of fighting , while the sun rose , the Ottomans had predicted an opening in the center of the Austrian attack and attacked in force , before a counterattack by the Austrian cavalry , led by Eugene himself , not only pushed them back but took the trenches , throwing the Ottoman camp into turmoil and causing the soldiers to flee . After 10 hours of fighting , the battle was won by the Austrians . The garrison of Belgrade surrendered after the defeat of the army in exchange for safe passage from the city . Ottoman losses were approximately 20 , 000 men and a large amount of equipment , ammunition and artillery . Implications . Belgrade fell into the hands of the Austrians , and a year later , the Peace Passarowitz ( July 2 , 1718 ) was signed by Austria which obtained at the expense of the Ottoman Empire , the Banat , Belgrade , the Serbia north , the Wallachia and other neighboring areas . The Empire reached its maximum expansion and the Balkans . Belgrade remained a territory under the domination of Austria for over twenty years , but on July 22 , 1739 , the Austrian army , commanded by the Field Marshal George Oliver Wallis was defeated near Belgrade , at the Battle of Grocka by the Ottoman army led by İvaz Mehmet Pasha . As a result of the Treaty of Belgrade ( September 1739 ) , the city and all the territories acquired at the Treaty of Passarowitz except Banat were returned to Ottoman rule .