In 1529, Vienna was besieged by the Ottoman Turks for the first time (the First Turkish Siege), although unsuccessfully. The city, protected by medieval walls, only barely withstood the attacks, until epidemics and an early winter forced the Turks to retreat. The siege had shown that new fortifications were needed. Following plans by Sebastian Schrantz, Vienna was expanded to a fortress in 1548. The city was furnished with eleven bastions and surrounded by a moat. A glacis was created around Vienna, a broad strip without any buildings, which allowed defenders to fire freely. These fortifications, which accounted for the major part of building activities well into the 17th century, became decisive in the Second Turkish Siege of 1683, as they allowed the city to maintain itself for two months, until the Turkish army was defeated by the army led by the Polish King John III Sobieski. This was the turning point in the Turkish Wars, as the Ottoman Empire was pushed back more and more during the following decades.