Gardoš Fortress, also known as the Zemun Fortress or the Citadela, is the oldest preserved part of Old Zemun and is considered one of Belgrade's best scenic viewpoints. The existing walls are originating from the 14th and the 15th century. The fortress was built as part of the Hungarian project of restoring or building fortresses on their southern borders, including today also ruined but surviving Kupinik and Slankamen, as a response to the incoming Ottoman invasion. Gardoš had a major role in 1456 Siege of Belgrade, when Hungarian forces headed by John Hunyadi repelled the Ottomans, and 1521 Siege of Belgrade, when the Ottomans, under the leadership of Sultan Suleiman the Magnificent conquered both Belgrade and Zemun. The entire garrison stationed at Gardoš Fortress, headed by the Šajkaši troops, was killed in the fighting and the fortress was the last stand of the entire battle. A 1608 miniature by Maximilian Prandstatter shows the castle fully preserved, complete with the roof. Representations of the Zemun skyline in the later 17th century, however, show only ruins.