The island is the home of Nilov Monastery, which was founded by Saint Nilus in 1594, and previously welcomed up to 40,000 pilgrims each year. Today the monastery complex remains as one of the most impressive ensembles of Neoclassical architecture in Eastern Europe. Some of its churches date back to the 17th century, a graceful embankment was completed by 1812, and a large cathedral was built in 1821-25.
During World War II, Nilov Monastery was the site of a NKVD camp which held approximately 7,000 Polish prisoners of war who had been taken captive by the Soviet Union as a result of the Molotov-Ribbentrop Pact. Almost all of the prisoners were subsequently executed in April 1940 in Kalinin (now Tver) and then buried in mass graves in Mednoye, an act which became known as the Katyn Massacre. Amongst those killed were Polish officers, lawyers, policemen, teachers, doctors, and other members of the intelligentsia.