Calvi wrote a letter of warning to Pope John Paul II on 5 June 1982, two weeks before the collapse of Banco Ambrosiano, stating that such an event would "provoke a catastrophe of unimaginable proportions in which the Church will suffer the gravest damage." The correspondence confirmed that illegal transactions were common knowledge among the top affiliates of the bank and the Vatican. Banco Ambrosiano collapsed in June 1982 following the discovery of debts between US$700 million and US$1.5 billion. Much of the money had been siphoned off through the Vatican Bank, which owned ten percent of Banco Ambrosiano and was their main shareholder.