Ostashkov (Оста́шков) is a town and the administrative center of Ostashkovsky District in Tver Oblast, Russia, on a peninsula at the southern shore of Lake Seliger, west of Tver, the administrative center of the oblast. Population: The island of Klichen was first mentioned in a letter sent by Grand Duke Algirdas of Lithuania to the Ecumenical Patriarch of Constantinople in 1371. After the island was pillaged by Novgorod pirates several years later, two of Klichen's surviving inhabitants, Ostashko and Timofey, moved to the mainland, where they founded the villages Ostashkovo and Timofeyevo, respectively. The former belonged to the Moscow Patriarchs, and the latter—to the Joseph-Volokolamsk Monastery. In 1770, both villages were merged into the town of Ostashkov. Ostashkov is commonly regarded as one of the finest Russian provincial towns. Its main streets were laid out in Neoclassical style after the plans of Ivan Starov (1772). Local landmarks include the Ascension Church (1689), the Trinity Cathedral (1697), the Monastery of the Sign (1673, 1730s, 1880s), and the mid-18th century Zhitny Cloister. There is also a fanciful column erected by people of Ostashkov in 1787 to mark a spot where a wooden fort (1587) used to stand. The town's pleasant architecture and attractive setting by the lake combine to make Ostashkov one of the most popular resorts in Western Russia. The well-known Nilov Monastery is on Stolobny Island, about north from Ostashkov. It was the place where the Ostashkov Special Camp of the NKVD was and where roughly 6,300 Polish policemen and prisoners of war were kept before they were executed in Tver. Approximately 4,300 of their comrades, held in Kozelsk, were around this time executed in Smolensk Oblast, in what is now known as the Katyn massacre. In 1772, Ostashkov was granted town status, and Ostashkovsky Uyezd of Novgorod Governorate was established, with the seat in Ostashkov. In 1775, Tver Viceroyalty was formed from the lands which previously belonged to Moscow and Novgorod Governorates, and the area was transferred to Tver Viceroyalty, which in 1796 was transformed to Tver Governorate.