Heroes, the Umschlagplatz, fragments of the ghetto wall on Sienna Street and a mound in memory of the Jewish Combat Organization. Many places commemorate the heroic history of Warsaw such as Pawiak, a German Gestapo prison now occupied by a Mausoleum of Memory of Martyrdom and a museum. The Warsaw Citadel, a 19th-century fortification built after the defeat of the November Uprising, was a place of martyrdom for the Poles. Another important monument, the statue of Little Insurrectionist located at the ramparts of the Old Town, commemorates the children who served as messengers and frontline troops in the Warsaw Uprising, while the Warsaw Uprising Monument by Wincenty Kućma was erected in memory of the largest insurrection of World War II. In Warsaw there are many places connected with the life and work of Frédéric Chopin who was born near the city in Żelazowa Wola. The heart of the Polish composer is sealed inside Warsaw's Holy Cross Church. During the summer time the Chopin Statue in Łazienki Park is a place where pianists give concerts to the park audience. Also many references to Marie Curie, her work and her family can be found in Warsaw; Curie's birthplace at the Warsaw New Town, the working places where she did her first scientific works and the Radium Institute at Wawelska Street for the research and the treatment of which she founded in 1925. Flora and fauna Green space covers almost a quarter of Warsaw's total area. These range from small neighborhood parks and green spaces along streets or in courtyards, to tree-lined avenues, large historic parks, nature conservation areas and urban forests at the fringe of the city. There are as many as 82 parks in the city; the oldest ones were once part of representative palaces and include the Saxon and Krasiński Gardens, Łazienki Park (Royal Baths Park) and Wilanów Palace Parkland. The Saxon Garden, covering an area of 15.5 ha, formally served as a royal garden to the now nonexistent Saxon Palace. In 1727, it was made into one of the world's first public parks and later remodelled in the forest-like English style. The Tomb of the Unknown Soldier is situated at the east end of the park near the central fountain, on Piłsudski Square. With its benches, flower carpets and a central pond, the Krasiński Palace Garden was once a notable strolling destination for most Varsovians. The Łazienki Park covers