Austrian gun depot) and Sveta Petka are also located in this area, as is the Belgrade Planetarium. The modern church of Sveta Petka was projected by architect Momir Korunović. Construction began in the first half of the 1930s, on the location of an old chapel. It was consecrated on 27 October 1937, the feast day of Parascheva of the Balkans, called Petka in Serbian. During the tenure of mayor Dragan Đilas (2008–13), the idea of expanding the zoo to Donji Grad, which it occupied prior to the World War II, resurfaced, but the experts were against it. The urban plan for the fortress from 1965 already projected the complete relocation of the zoo outside of the fortress, to some suburban locations, which in later plans included Veliko Blato, Stepin Lug or Jelezovac. The expansion of the zoo would cut the pedestrian communication between the Danube's and Sava's parts of the fortress, which was already cut in 1949 but was restored in 2009 with the reconstruction and opening of the Sava Gate. Also, it would prevent the exploration of Donji Grad, which is still largely unexplored and leave the Gate of Charles VI, a masterpiece of Balthasar Neumann, within the zoo itself. As of 2017, the zoo was not relocated but the idea of expansion was dropped, too. Apart from the protection of the fortress as the cultural monument, parts of the Lower Town, and the slope which separates it from the Upper Town are protected as a natural monument. The area was included in the first protection of the fortress in 1946. In 1968 two areas were separately protected: "Maritime Neogenic Ridge - profile under the Pobednik monument in Kalemegdan" and "Geological-geographical layers at Kalemegdan locality, at the Pobednik monument". Serbian Environmental Agency drafted a study on the area and submitted it to the government in 2017. In February 2021, the government joined two previously protected area and expanded the protected area to , establishing a natural monument of Kalemegdan Sandbank. The area is a unique geological feature in Serbia, as the remains of the sea ridge of the oldest stage in the history of the Pannonian Sea. Those include sediments originating from the middle, Badenian stage of the Miocene period. The cliffs are thought to have a historical importance also - the Slavic name of Belgrade, white town, according to one of the theories, originates from the exposed white