In the first half of the 17th century, kings of the House of Vasa turned the Jasna Góra Monastery into a modern Dutch-style fortress. During the Swedish invasion of Poland in 1655, the monastery was one of the pockets of Polish resistance against the Swedish armies (for more information, see Siege of Jasna Góra). The town of Częstochowa was almost completely destroyed by Swedish soldiers. It has been estimated that the town lost 50% of the population, and 60% of houses. But the town suffered less severe destruction than such area towns as Przyrów, Olsztyn and Mstów. It took several years for Częstochowa to recover from extensive losses. As late as in the 1680s there still were ruined houses in the town.