On 2 July 1947, the Polish government passed a law establishing a state memorial to remember "the martyrdom of the Polish nation and other nations in Oswiecim". The museum established its exhibits at Auschwitz I; after the war, the barracks in Auschwitz II-Birkenau had been mostly dismantled and moved to Warsaw to be used on building sites. Dwork and van Pelt write that, in addition, Auschwitz I played a more central role in the persecution of the Polish people, in opposition to the importance of Auschwitz II to the Jews, including Polish Jews. An exhibition opened in Auschwitz I in 1955, displaying prisoner mug shots; hair, suitcases, and shoes taken from murdered prisoners; canisters of Zyklon B pellets; and other objects related to the killings. UNESCO added the camp to its list of World Heritage Sites in 1979. All the museum's directors were, until 1990, former Auschwitz prisoners. Visitors to the site have increased from 492,500 in 2001, to over one million in 2009, to two million in 2016.