Siege of Vienna

Siege of Vienna Combatants

The Siege of Vienna was fought between the Holy Roman Empire and the Ottoman Empire. Let's look at who comprised the two combatant powers.

The Ottoman Empire Suleiman the Magnificent

Suleiman I assumed the sultanate of the Ottoman Empire in 1520 and began his imperial expansions into Eastern and Central Europe swiftly, conquering Belgrade (1521), Rhodes (1522) and part of Hungary in 1526.

Fig. 1 - Suleiman the Magnificent became Sultan of the Ottoman Empire in 1520 and had ambitious designs of imperial expansion throughout Europe, pitting him against the Holy Roman Empire of the Habsburgs.

The Battle of Mohacs (August 1526) saw Suleiman I easily defeat the Hungarian Army. The king of Hungary and Bohemia, Louis II, died in the conflict. Suleiman did not annex the whole of Hungary to the Ottoman Empire immediately after the conflict, and left the throne vacant.

The Hungarian throne was contested by two people. The first was Ferdinand I, the younger brother of Charles V, the Holy Roman Emperor. The second was John Zápolya, the voivode of the Hungarian territory of Transylvania. The voivode was the highest military rank of a region, and was a title typically used in eastern Europe.

Suleiman agreed to support Zápolya's ascension to the throne of Hungary, so long as he was a vassal of the Ottoman Empire. After the Battle of Mohacs, Suleiman advanced in September 1526 to sack and pillage the Hungarian capital of Buda (part of modern-day Budapest) to secure the capital for the new vassal King John I.

With Hungary acting as a buffer country between Habsburg Austria and the Ottoman Empire, Suleiman continued his advances into Austrian territory with the aim of expanding his Empire into Eastern and Central Europe against the Habsburg's Holy Roman Empire.

The (Habsburg) Holy Roman Empire Ferdinand I

Whilst Suleiman made gains through Eastern Europe, the Habsburg Holy Roman Emperor, Charles V, was preoccupied with the Western parts of the Empire in Spain and France. In 1521, he appointed his younger brother, Ferdinand I, as the Archduke of Austria and entrusted him with the protection of the Eastern parts of the Holy Roman Empire in Austria.

Fig. 2 - Ferdinand I became Archduke of Austria in 1521. Ferdinand would eventually succeed his brother in 1556 as Holy Roman Emperor

After the death of his brother-in-law King Louis II in 1526, Ferdinand laid claim to both the throne of Bohemia and Hungary. He succeeded in Bohemia, but had competition from John Zápolya who was supported by Suleiman.

With control of Hungary divided between the Habsburgs and Ottomans, Ferdinand attempted to raise support from Charles V's Imperial Army and German princes to defend Austria, which now shared a border directly with the Ottomans. His attempts were mostly ignored as conflicts arose in Western Europe, leaving Austria vulnerable. Ferdinand fled Vienna to Habsburg Bohemia once Suleiman began advancing from Ottoman Bulgaria in May 1529. Commanders Niklas Graf Salm and Wilhelm von Roggendorf organised the defence of Vienna during the subsequent Ottoman siege in September 1529.

First Siege of Vienna

Suleiman's first advances on Vienna began in May 1529 when his army of more than 100,000 troops left Ottoman Bulgaria. The rains were particularly heavy that season, meaning that Suleiman's route was tricky. Large artillery such as canons had to be left behind in the mud, and many of the Ottomans' camels also perished.

In August, Suleiman's troops met with King John I's army at Mohacs and marched together to recapture areas the Ottomans had held since the Battle of Mohacs in 1526, including the Hungarian capital of Buda in September 1529. The recapture of Buda was renowned as a brutal massacre to secure the city once again for the Ottoman Empire.

News of Suleiman's advances reached Vienna, who, commanded by Graf Salm and von Roggendorf, began to prepare the city for the siege by reinforcing the walls and blocking off the entrances. When the Ottomans arrived on 27 September, they were disadvantaged from their journey, lacking the heavy equipment for siege warfare and with many troops in a poor state of health from the march.

Fig. 3 - Although Suleiman the Magnificent's troops significantly outnumbered the Austrian army during the 1529 Siege of Vienna, the prior weather conditions had weakened the Ottoman army. Furthermore, the use of long spears atop Vienna's walls successfully fended off the attackers despite their superior number

On 6 October, 8,000 Austrian troops left the city to disrupt the Ottomans' mining efforts to the walls. Although the Austrians succeeded in destroying the mines, many were killed in the congested retreat behind the city walls.

On 11 October, more rain dampened Ottoman gunpowder supplies and their spirits, leading Suleiman to call a meeting the following day to discuss their retreat after one last attack on 13 October. Their efforts had been marred significantly by the poor weather, which had depleted their supplies so that a long siege was untenable. The Austrians managed to defend the walls with long spears to pick off Ottoman ladders.

Suleiman began his retreat on 14 October, but was caught with heavy snow, making the journey back particularly challenging.

Second Siege of Vienna

Despite the failure of Suleiman's first attempt to take Vienna, his final attack on 13 October 1529 is deemed by some historians as an attempt to weaken the city for a future attack. Ferdinand launched a campaign in 1530 to recapture the cities and forts that Suleiman had taken in the lead up to the first Siege of Vienna. He was unsuccessful at regaining Buda from John I, but assumed control of strategic forts along the Danube River in Habsburg Hungary.

Suleiman responded by launching another campaign to besiege Vienna in 1532. The Ottomans amassed another army of around 120,000 and began marching. When Suleiman reached Osijek in Slavonia (a region of Croatia), he headed West into Habsburg Hungary rather than up to Buda. Suleiman's rapid advances through Hungary meant Ferdinand withdrew his army back to Austria.

Fig. 4 - The Siege of Köszeg demonstrated the unbelievable defence of Croatians against the Ottoman army. As Suleiman was delayed at Köszeg, Ferdinand managed to assemble an army at Vienna, which helped to deter Suleiman into retreat

Suleiman reached the Croatian fort of Köszeg on 5 August 1532, which was defended by less than 1,000 troops due to Ferdinand's withdrawal. The Ottomans besieged Köszeg for 25 days, and the Croatian force successfully rebuked every attack. Suleiman had hoped that the siege would draw Ferdinand's army out into a battle between the forces, but Köszeg received no aid.

After the 25-day siege, Suleiman eventually retreated once the seasonal rain began, fearing a similar fate as his previous attempt to take Vienna. The vulnerability of Vienna was made clear to Charles V, who sent 80,000 Imperial troops to aid Ferdinand in the city. The weather, the delay due to Köszeg, and the amassed Imperial army led Suleiman to retreat to Constantinople (modern-day Istanbul). He decimated several Habsburg cities during his retreat through the Austrian region of Styria.

Importance of the Siege of Vienna

Suleiman the Magnificent's attempted Siege of Vienna led to repercussions of the relationship between the Habsburgs and the Ottomans and affected the future of the Eastern European border between the Empires. Let's look at the importance of the Siege of Vienna.

Protestant Reformation

As the Ottoman Empire was primarily an Islamic Caliphate, the Holy Roman Empire's defence of Vienna was viewed as a Catholic victory by the Church. As the Siege of Vienna occurred during the era of Protestant Reformation, it was used as propaganda by both sides of the Reformation.

The victory over the siege of Vienna meant the Habsburgs earned favour as Catholic defenders, helping the Counter-Reformation. The Church established several new monasteries in Vienna to celebrate the victory for Catholicism.

Treaty of Constantinople

After the two attempts by the Ottomans to take control of Vienna, Ferdinand I and Suleiman reached a truce at Constantinople regarding Hungary in 1533. The truce agreed:

• Ferdinand would hold the lands he recaptured after the second attempted Siege of Vienna in 1532.

• Hungary would be divided between the Ottomans and Habsburgs.

• Ferdinand would be regarded as the King of Germany, whilst Charles V was King of Spain. Suleiman would be the only one referred to as Emperor.

Ferdinand and John I agreed the secret Treaty of Nagyvárad in 1538. It agreed that Ferdinand would assume the kingship of Hungary after King John I's death. However, after the treaty, John I's wife had a child. When John died in 1540, his son succeeded him. As a result, Ferdinand renewed his claim to the Hungarian throne and conflict arose again between Habsburgs and Ottomans.

Little War of Hungary

Ottomans and Habsburgs continued to fight over Hungary for decades. Hungary acted as a strategic buffer zone between the Empires, and for the Habsburgs stopped Ottoman expansion into Europe.

The Siege of Vienna allowed Suleiman to better establish his vassal state with King John I as a buffer against the Holy Roman Empire. However, conflicts still arose throughout the 16^th century between the Empires for control of Hungary.

Suleiman proceeded to annex Hungary in two campaigns in 1541 and 1543. The result was a firmer division of Hungary into Royal Hungary (Habsburg), Turkish Hungary (Ottoman), and the Principality of Transylvania (Ottoman vassal state).