Some historians consider Ostashkov to bear city status from 1770, after Catherine the Great issues her decree. These scientists are not quite right, despite the fact that two settlements existed before the Royal decree. Documents of 16th-17th centuries mention the town of Klichen, which has full rights to be the parent of two Ostashkov settlements. Said town is located on an island near modern city of Ostashkov, leaving its name to this island.

The island now hides remaining traces of the ancient Klichen, which stood on the northwest coast of the island. Favourite legend of local population tells a story of a fisherman, named Evstaphy, the only survival from destroyed Klichen, who moved to a peninsula near the island and settled there (central street of modern Ostashkov now bears his name). Ostashkov settlement grows quite rapidly by attracting new settlers, who found other villages.

In the end of 15th century Ostashkov villages turn to big settlements, and in 1587 their population builds a fortress to protect them from possible Lithuanian attacks. However, these walls fail to protect the town during Polish and Lithuanian hordes. After invaders are banished from the town, Ostashkov starts expanding rapidly and a new settlement, where boats are made, appears. Dwellers of the Moscow region are afraid of a new invasion and hurry to build fortifications in towns, bordering with Lithuania. Ostashkov is among these towns, and in 1626 the fortress is finished. However, hastily built constructions didn’t live long, and in three years (1651-1653) another fortress is erected around the town before the war with Poland. Fate of the third fort is the same – in 1676 its walls and towers disappear in the great fire. However, Ostashkov is still an important strategic border settlement, and forth and the last fortress protects the town till 1711, when it perishes in fire and is never rebuild.

In the end of 17th century Ostashkov turns into a large city with rapidly growing population and developing trade. Close Lithuanian border doesn’t prevent city’s development. Ostashkov actively trades with other bordering cities, as well as with Poland and Lithuania. Many Russian cities of the late 17th century, including Ostashkov, show simultaneous development of trade and building activities. Two settlements of Ostashkov are another reason for building boom in the area. In 1677 citizens start erecting the Voskresensky (after Resurrection) cathedral, one of the biggest churches in the whole Tver region, in one of the city’s parts, and in 1685 foundation of another cathedral, named Troitsky (after Trinity), is laid in the second part of Ostashkov. Both cathedrals later obtain bell towers. Their appearance change with time – interiors are painted and reconstructed.

After Ostashkov obtains city status in 18th century, it changes a lot. City centre boasts stone cathedrals, surrounded with randomly built houses of city dwellers. Behind the fortress gardens are located, and a large number of fishermen dwells along the south-east coast of the Seliger Lake. Ostashkov hosts blacksmiths and shoemakers, chasers and goldsmiths, woodworkers, wood-carvers, painters and even watchmakers. Painting is hereditary profession in Ostashkov – 42 painters live in the city in the forties of 18th century. They are famous for their works and are invited to Moscow, Saint Petersburg and other Russian cities to paint for Royal family and churches. City merchants take mote and more active part in political life of the city. Ostashkov’s exterior obtains new luxurious stone houses, which merchants build for themselves and their families.

Twenties of the following century bring drastic changes to the city’s appearance. New houses are built according classicism and look like one- or two-storeyed mansions with mezzanines. Other houses are rebuilt according new fashion trends. Original Ostashkov buildings start slowly disappearing, and new houses look ordinary, lacking imagination. Former splendour of the city grows dim, and city development stops. City merchants, who form Ostashkov’s prosperity, slowly become petty, lose everything and degrade.

However, the city obtains a hospital, public and religious schools, a library, a theatre, a founding hospital, a school for young ladies, city gardens and brass band and etc. Almost every citizen is literate, but all prosperity is for show.

In second part of the 19th century Ostashkov grows poor and turns into ordinary district town, boasting its past and having nothing in present. Today Ostashkov and its surroundings are open for tourists and visitors.