In 1655, Poland was almost entirely overrun by the forces of Sweden's King Charles X. Only the area around the monastery remained unconquered. Somehow, the monks of the monastery managed to successfully defend the painting against a forty-day siege and eventually they were able to drive out the invaders of all of Poland. After this remarkable turn of events, Our Lady of Czestochowa became the symbol of Polish national unity and was crowned Queen of Poland. The King of Poland placed the country under the protection of the Blessed Mother. A more recent legend surrounding the painting involves the threat of a Russian invasion. In 1920, the Russian army was spotted as they amassed on the banks of the Vistula River, threatening to attack Warsaw, when an image of the Virgin was seen in the clouds over the city. The Russian troops withdrew on seeing this vision. There have been other reports for centuries of miraculous events such as spontaneous healings occurring to those who made pilgrimages to see the painting, known as the "Black Madonna" because of the soot residue that discolors the painting. The soot is the result of centuries of votive lights and candles burning in front of the painting. With the decline of communism in Poland, pilgrimages to the Black Madonna have increased dramatically.