In the spring of 1529, Suleiman mustered a large army in Ottoman Bulgaria, with the aim of securing control over all of Hungary and reducing the threat posed at his new borders by Ferdinand I and the Holy Roman Empire.
Estimates of Suleiman's army vary widely from 120,000 to more than 300,000 men, as mentioned by various chroniclers.
As well as numerous units of Sipahi, the elite mounted force of the Ottoman cavalry, and thousands of janissaries, the Ottoman army incorporated a contingent from Moldavia and renegade Serbian warriors from the army of John Zápolya.
Suleiman acted as the commander-in-chief (as well as personally leading his force), and in April he appointed his Grand Vizier (the highest Ottoman minister), a Greek former slave called Ibrahim Pasha, as Serasker, a commander with powers to give orders in the sultan's name.

Suleiman launched his campaign on 10 May 1529 and faced numerous obstacles from the onset.
The spring rains that are characteristic of south-eastern Europe and the Balkans were particularly heavy that year, causing flooding in Bulgaria and rendering parts of the route used by the army barely passable.
 Many large-calibre cannons and artillery pieces became hopelessly mired or bogged down, leaving Suleiman no choice but to abandon them, while camels brought from the empire's Eastern provinces, not used to the difficult conditions, were lost in large numbers.
Sickness and poor health became common among the janissaries, claiming many lives along the perilous journey.

Suleiman arrived in Osijek on 6 August.
On the 18th he reached the Mohács plain, to be greeted by a substantial cavalry force led by John Zápolya (which would later accompany Suleiman to Vienna), who paid him homage and helped him recapture several fortresses lost since the Battle of Mohács to the Austrians, including Buda, which fell on 8 September.
The only resistance came at Pozsony, where the Turkish fleet was bombarded as it sailed up the Danube.
In the spring of 1529, Suleiman mustered a large army in Ottoman Bulgaria, with the aim of securing control over all of Hungary and reducing the threat posed at his new borders by Ferdinand I and the Holy Roman Empire. Estimates of Suleiman's army vary widely from 120,000 to more than 300,000 men, as mentioned by various chroniclers. As well as numerous units of Sipahi, the elite mounted force of the Ottoman cavalry, and thousands of janissaries, the Ottoman army incorporated a contingent from Moldavia and renegade Serbian warriors from the army of John Zápolya. Suleiman acted as the commander-in-chief (as well as personally leading his force), and in April he appointed his Grand Vizier (the highest Ottoman minister), a Greek former slave called Ibrahim Pasha, as Serasker, a commander with powers to give orders in the sultan's name.
Suleiman launched his campaign on 10 May 1529 and faced numerous obstacles from the onset. The spring rains that are characteristic of south-eastern Europe and the Balkans were particularly heavy that year, causing flooding in Bulgaria and rendering parts of the route used by the army barely passable.  Many large-calibre cannons and artillery pieces became hopelessly mired or bogged down, leaving Suleiman no choice but to abandon them, while camels brought from the empire's Eastern provinces, not used to the difficult conditions, were lost in large numbers. Sickness and poor health became common among the janissaries, claiming many lives along the perilous journey.
Suleiman arrived in Osijek on 6 August. On the 18th he reached the Mohács plain, to be greeted by a substantial cavalry force led by John Zápolya (which would later accompany Suleiman to Vienna), who paid him homage and helped him recapture several fortresses lost since the Battle of Mohács to the Austrians, including Buda, which fell on 8 September. The only resistance came at Pozsony, where the Turkish fleet was bombarded as it sailed up the Danube.
Siege of Vienna