Sliven (Bulgarian: Сливен) is the eighth-largest city in Bulgaria and the administrative and industrial centre of Sliven Province and municipality. Sliven is famous for its Bulgarian Haiduts who fought against the Ottoman Turks in the 19th century and is known as the "City of the 100 Voyvodi", a Voyvoda being a leader of Haiduts. The famous rocky massif Sinite Kamani (Сините камъни, "The Blue Rocks") and the associated national park, the fresh air and the mineral springs offer diverse opportunities for leisure and tourism. Investors are exploring the opportunity to use the famous local wind (Bora) for the production of electricity. Another point of interest and a major symbol of the city as featured on the coat of arms, is over thousand-year-old Stariyat Briast (Старият Бряст, "The Old Elm"), a huge Smooth-leaved Elm in the center of the city. In times of the Ottoman rule Turkish officials used to hang Bulgarian revolutionaries on it. Today the city is helping the tree live on by frequent evaluations and reinforcing its base. It was elected Bulgarian tree of the year in 2013. On 19 March 2014 the results of online poll were revealed at a ceremony in the European Parliament. The Old Elm was voted European tree of the year 2014. Sliven Peak on Livingston Island in the South Shetland Islands, Antarctica is named after Sliven. Sliven is located 300 km east of Bulgaria"s capital Sofia, 100 km from Bourgas, the country"s largest commercial port, 130 km from the border with Greece and 130 km from the border with Turkey. It is located in close proximity to the cities of Yambol and Nova Zagora.