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. There have been protracted disputes over the perceived Christianization of the site. Pope John Paul II celebrated mass over the train tracks leading to Auschwitz II-Birkenau on 7 June 1979 and called the camp "the Golgotha of our age", referring to the crucifixion of Jesus. More controversy followed when Carmelite nuns founded a convent in 1984 in a former theater outside the camp's perimeter, near block 11 of Auschwitz I, after which a local priest and some survivors erected a large cross—one that had been used during the pope's mass—behind block 11 to commemorate 152 Polish inmates shot by the Germans in 1941. After a long dispute, Pope John Paul II intervened and the nuns moved the convent elsewhere in 1993. The cross remained, triggering the "War of the Crosses", as more crosses were erected to commemorate Christian victims, despite international objections. The Polish government and Catholic Church eventually agreed to remove all but the original. On 4 September 2003, despite a protest from the museum, three Israeli Air Force F-15 Eagles performed a fly-over of Auschwitz II-Birkenau during a ceremony at the camp below. All three pilots were descendants of Holocaust survivors, including the man who led the flight, Major-General Amir Eshel. On 27 January 2015, some 300 Auschwitz survivors gathered with world leaders under a giant tent at the entrance to Auschwitz II to commemorate the 70th anniversary of the camp's liberation. Museum curators consider visitors who pick up items from the ground to be thieves, and local police will charge them as such; the maximum penalty is a 10-year prison sentence. In 2017 two British youths from the Perse School were fined in Poland after picking up buttons and shards of decorative glass in 2015 from the "Kanada" area of Auschwitz II, where camp victims' personal effects were stored. The Arbeit Macht Frei sign over the main camp's gate was stolen in December 2009 by a Swedish former neo-Nazi and two Polish men. The sign was later recovered. In 2018 the Polish government passed an amendment to its Act on the Institute of National Remembrance, making it a criminal offence to violate the "good name" of Poland by accusing it of crimes committed by Germany in the