Events during the siege

The main Turkish army finally invested Vienna on July 14. On the same day, Kara Mustafa sent the traditional demand for surrender to the city.

Ernst Rü diger Graf von Starhemberg, leader of the remaining 11, 000 troops and 5, 000 citizens and volunteers with 370 cannons, refused to capitulate. Only days before, he had received news of the mass slaughter at Perchtoldsdorf, a town south of Vienna whose citizens had handed over the keys of the city after having been given a similar choice.

The Viennese had demolished many of the houses around the city walls and cleared the debris, leaving an empty plain that would expose the Turks to defensive fire if they tried to rush the city. Kara Mustafa Pasha solved that problem by ordering his forces to dig long lines of trenches directly toward the city, to help protect them from the defenders as they advanced steadily toward the city.

Although the Turks had 300 good cannons, the fortifications of Vienna were very strong and up to date, and the Turks had to invent a more effective use for their gunpowder: mining. Tunnels were dug under the massive city walls to blow them up with explosives.

The Ottomans had essentially two options to take the city: the first, an all-out assault, was virtually guaranteed success since they outnumbered the defenders almost 20-1. The second was to lay siege to the city, and this was the option they chose.

This seems against military logic, but assaulting properly defended fortifications has always resulted in very heavy casualties for the attackers. A siege was a reasonable course of action to minimise casualties and capture the city intact, and in fact it nearly succeeded. What the Ottomans did not take into account however was that time was not on their side. Their lack of urgency at this point, combined with the delay in advancing their army after declaring war, eventually allowed a relief force to arrive. Historians have speculated that Kara Mustafa wanted to take the city intact for its riches, and declined an all-out attack in order to prevent the right of plunder which would accompany such an assault.

The Ottoman siege cut virtually every means of food supply into Vienna, and the garrison and civilian volunteers suffered extreme casualties. Fatigue became such a problem that Graf Ernst Rü diger von Starhemberg ordered any soldier found asleep on watch to be shot. Increasingly desperate, the forces holding Vienna were on their last legs when in August, Imperial forces under Charles V, Duke of Lorraine beat Imre Thö kö ly of Hungary at Bisamberg, 5km northeast of Vienna.

On 6 September, the Poles crossed the Danube 30km north west of Vienna at Tulln, to unite with the Imperial forces and additional troops from Saxony, Bavaria, Baden, Franconia and Swabia who had answered the call for a Holy League that was supported by Pope Innocent XI. Only Louis XIV of France, Habsburg's rival, not only declined to help, but used the opportunity to attack cities in Alsace and other parts of southern Germany, as in the Thirty Years' War decades earlier.

During early September, the experienced 5, 000 Turkish sappers repeatedly blew up large portions of the walls, the Burg bastion, the Lö bel bastion and the Burg ravelin in between, creating gaps of about 12m in width. The Austrians tried to counter by digging their own tunnels, to intercept the depositing of large amounts of gunpowder in subterranean caverns. The Turks finally managed to occupy the Burg ravelin and the Nieder wall in that area on 8 September. Anticipating a breach in the city walls, the remaining Austrians prepared to fight in Vienna itself.