The Siege of Vienna: Limits on Ottoman Power

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In 1529, the Ottoman Empire made their first attempt to capture the city of Vienna, in what proved to be the height of Ottoman expansion into Europe. The campaign as a whole was a success for the Ottomans: they gained complete control over Hungary, seizing lands and installing a puppet king, John Zápolya. However, the failure of the Siege of Vienna ultimately exposed long-term constraints on Ottoman power in Europe.

The events that led the Ottomans to the heart of Austria started with victory in Hungary in 1526. The Ottoman Sultan Suleiman I’s forces had defeated Hungary in battle, killing their King, Louis II. The resulting power vacuum drew three powers into the conflict: the Ottomans, who had taken control of the south of the kingdom; the Austrians, led by Archduke Ferdinand I of Austria; and John Zápolya, a Hungarian aristocrat seeking to be made king of Hungary.

Archduke Ferdinand’s claim to the Hungarian throne was based on his marriage to the sister of the deceased Louis, and Louis’s marriage to his. His powerbase was established in the northwest of Hungary and his capital in Pozsony. From there, he sought to conquer the rest of Hungary. The Austrians made significant progress, taking Buda, the historic capital, in 1527.

Meanwhile, Zápolya consolidated his force in Transylvania. However, he knew that he could not hope to defeat the Austrians and their Habsburg allies himself. Therefore, he turned to Suleiman and the Ottomans, pledging Hungary as an Ottoman vassal so long as they supported his claim as king.

Zápolya intended to stake his claim as Hungary’s ruler at the Battle of Tarcal in 1527: he was comprehensively beaten. The following year, Ferdinand took yet more Hungarian land with victory at the Battle of Szina, as Austria seized much of Hungary’s heartland. Zápolya fled to Poland after these defeats and desperately called on Suleiman to drive Ferdinand out.

Suleiman increasingly realised that Ottoman control over Hungary required Ottoman military action, not merely symbolic support of a vassal king. Therefore, in the spring of 1529, Suleiman raised an army, estimated to number up to 300,000 by contemporaries (but more likely around 120,000) and set out on 10 May on his march through Eastern Europe.

The spring rains were very heavy that year, causing significant flooding and rendering much of their route so muddy it was near-impassable; many of their heavier cannons had to be left behind, which would later prove costly. Many camels from the eastern part of the empire, not used to these conditions, died, and disease similarly became rife among the Ottoman forces. These troubles during their march north weakened them significantly.

Nonetheless, they continued, joining with the forces of Zápolya en route. Indeed, the struggles of their earlier march north did not seem to affect the Ottomans much in the early stages of the campaign, as they retook many towns and fortresses from the Austrians with little resistance. Soon, Suleiman and his army were within striking distance of Vienna.

By this point, Western Europe had began to take great notice of the Ottoman advance and the threat it posed. Though the Austrian Archduke Ferdinand had fled Vienna, his capital, the Charles V, the elected King of Germany, provided a defensive force, which consisted of 17,000 mercenaries. This assisted the local garrisons in preparing for the defence of the city.

The mercenaries, led by Nicholas, Count of Salm, began organising the reinforcement of the city’s 300-year-old walls and blocked the gates; they also razed buildings around the city to avoid providing cover to their attackers. The discipline and experience of these soldiers proved crucial in the successful Austrian resistance.

The Ottomans arrived outside the walls of Vienna on 24 September 1529. By now, the long march into Austria had taken its toll: they were severely lacking in cavalry and artillery and many of their men were now sick. Of those fit to fight, roughly a third were light cavalrymen (Sipahis), of little use in siege warfare. Despite this, Suleiman’s forces still greatly outnumbered the defending army, perhaps as much as five to one, and were easily able to isolate the city from any incoming aid. Suleiman sent his terms for surrender to the city’s defenders. The garrison rejected them, and the siege began.

The Ottoman forces twice assaulted the walls at the start of the siege, and were twice easily repelled. As they had only light artillery left, they were unable to do any significant damage to the walls or city itself. They made limited progress.

Yet this was not the Ottomans’ main plan, instead a diversion to allow Ottoman sappers to dig deep trenches and tunnels below the city walls, where mines could be planted and detonated to bring the walls down. The defenders were prepared for this, though, having established a system of water buckets in the cellars along the city walls which would shake when the Ottomans dug beneath them – the Austrians were aware of all the Ottomans’ subterranean movements.

On 6 October, 8000 defenders of Vienna set out into these tunnels to destroy them all at once. The defenders took heavy losses due to the difficulties of retreating in such a confined space, but successfully repelled the majority of the Ottoman advances. Though one of the mines did successfully detonate close enough to the city walls to breach it, the defenders formed a pike wall at the breach and were able to repel the Ottoman assault.

Morale within the Ottoman camp was plummeting. Their efforts to breach the city had failed, they were running short on food and other vital supplies, and on 11 October the rain, so often the scorn of their campaign, returned. Thus, the Janissaries, the elite units of the army, demanded a decision on whether to abandon the siege. To this end, Suleiman held a council on the 12 October to discuss the matter.

They decided upon one final, massive attack upon the city to try to salvage the siege. On 14 October the full remaining force of the Ottoman army assaulted the city. However, the German mercenaries held the line with their disciplined pike line and musket fire, whilst the other defenders rained gunfire down on the attackers. The Ottomans saw the futility of their attack and called it off after a mere two hours.

The next day, with snow beginning to fall, the Ottomans withdrew from the siege. In total, the Ottomans lost around 15,000 men during the siege, whilst the defenders losses are largely unknown.

In spite of defeat at Vienna, Suleiman claimed an overall victory for the Ottomans. His goal was not to take the city but only the lands of Hungary; conquering Vienna would have been a bonus for an already successful campaign that greatly improved the Ottoman position in Europe.

However, the boundary established by defeat at Vienna would prove to be unsurpassable in later years. The difficulties of establishing lengthy supply lines and the harshness of European winters that had so plagued the 1529 mission precluded sustained Ottoman campaigns into Europe in general. Another attempted conquest of Vienna three years later was stopped short of the city and stalled until winter, at which point they had to turn back. For the next 150 years, Austrian-Ottoman tensions persisted in the region, with no further Ottoman progress, until they were finally driven back following a final unsuccessful siege of Vienna in 1683. While the first Siege of Vienna was a high watermark of Ottoman extension into Europe, it was also a turning point that demonstrated the logistical limits of Ottoman power.

Turnbull, S., 2003. The Ottoman Empire: 1326–1699. Osprey Publishing.