Siege of Vienna - Wikipedia

On September 24, 1529, Sultan Suleiman the Magnificent and his Ottoman troops arrive in Vienna, beginning of the siege. From the article:

"The inability of the Ottomans to capture Vienna in 1529 turned the tide against almost a century of conquest throughout eastern and central Europe. The Ottoman Empire had previously annexed Central Hungary and established a vassal state in Transylvania in the wake of the Battle of Mohács. According to Arnold J. Toynbee, "The failure of the first [siege of Vienna] brought to a standstill the tide of Ottoman conquest which had been flooding up the Danube Valley for a century past."[5]

There is speculation by some historians[6] that Suleiman's main objective in 1529 was actually to assert Ottoman control over the whole of Hungary, the western part of which (known as Royal Hungary) was under Habsburg control. The decision to attack Vienna after such a long interval in Suleiman's European campaign is viewed as an opportunistic manoeuvre after his decisive victory in Hungary. Other scholars[6] theorise that the suppression of Hungary simply marked the prologue to a later, premeditated invasion of Europe."