The Orthodox historian Bishop Arseny (Bryantsev) challenged the authenticity of the correspondence and, incidentally, points to the 50 letters of Cyril of Tsar Mikhail Fedorovich and Moscow Patriarch Philaret, stored in a Moscow archive of the main Ministry of Foreign Affairs and the evidence of Cyril's commitment to Orthodoxy, as well as in his 1622 letter in which he speaks of Protestantism as a blasphemous doctrine.[12]