The Apostolic constitution Antiqua Iudaeorum Improbitas (1581 and 1593) was an important part of the history of the relationship between the Italian Jews (or Jews living in Italy) and the Roman Inquisition. Thanks to this regulation, the Sacra Congregazione was finally and formally invested with full powers of control over the Jews to preserve those principles of law and faith quae sunt communia between Judaism and Christianity. This standard was suddenly used to watch over every aspect of Jewish life, from religious issues to both cultural and economic ones. Among these widely various cases, travels of the Jews in the Ottoman territories and conversions to Islam stand out; indeed, even the apostasy from Judaism was regarded as betrayal of those principles. Reading the spontaneous confessions of the Jews and the questions drawn up by the consultori on the basis of the legal literature and previous cases, it is possible to reflect from a new perspective both on the history of the Italian Jews in the Ghetto Age and on the history of the Roman Inquisition itself.
Keywords: Jews, Islam, Roman Inquisition, Travels, Leghorn.