Sevastopol is a port city in Ukraine, located on the Black Sea coast of the Crimea peninsula. The unique geographic location and navigation conditions of the city’s harbours make Sevastopol a strategically important naval point. It is also a popular seaside resort and tourist destination, mainly for visitors from the Commonwealth of Independent States (CIS) countries.  The trade and shipbuilding importance of Sevastopol's Port has been growing since the fall of the Soviet Union,[citation needed] despite the difficulties that arise from the joint military control over its harbours and piers. Sevastopol is also an important centre of marine biology research. In particular, studying and training of dolphins has been conducted in the city since the end of World War II. It was first conducted as a secret naval program to use the animals for special undersea operations. Sevastopol together with Kronstadt and Gibraltar is one of the most famous naval citadels in Europe. During the Soviet era, Sevastopol, became a so-called "closed city". This meant that any non-residents had to apply to the authorities for the temporary permit to visit the city. Once closed for tourists, Sevastopol - the second biggest Crimean city, started welcoming guests shortly after the Soviet Union break up. Located in a unique harbour, it was bound to become a navy base. The history of the city starts with the foundation of a Greek colony Chersonesus in 422 BC. Since then the city has been playing the key part in history and the development of the Crimea and the whole country. It is called the cradle of Russian Christianity as the place where Prince Vladimir was first of Russian rulers to adopt Christianity and from where the religion spread to Russian lands. After the decline of Chersonesus the area was not densely populated until Sevastopol was founded in 1783 as a naval base and fortress on the southern boundaries of the Russian Empire. Most of the city's history is linked to its mil...