Coat of arms of the Holy See with gold key in bend as described in Donald Lindsay Galbreath, A Treatise on Ecclesiastical Heraldry (W. Heffer and Sons, 1930), p. 9; Bruno Bernhard Heim, Heraldry in the Catholic Church: Its Origin, Customs and Laws (Van Duren 1978 ISBN 9780391008731), p. 54; Heraldry Society of Great Britain; Michel Pastoureau, "Keys" in Philippe Levillain, The Papacy: An Encyclopedia (Routledge 2002 ISBN 9780415922302), vol. 2, p. 891.
Donald Lindsay Galbreath, A Treatise on Ecclesiastical Heraldry (W. Heffer and Sons, 1930), p. 9;
Bruno Bernhard Heim, Heraldry in the Catholic Church: Its Origin, Customs and Laws (Van Duren 1978 ISBN 9780391008731), p. 54;
Heraldry Society of Great Britain;
Michel Pastoureau, "Keys" in Philippe Levillain, The Papacy: An Encyclopedia (Routledge 2002 ISBN 9780415922302), vol. 2, p. 891
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