No one today can contemplate writing serious medieval history, or carrying out any major research project, certainly from the thirteenth century onwards, without recourse to some part of the Vatican Archives. The Vatican Archives is the oldest and the largest collection of archives in Europe, the major fount of knowledge and the most important (from a European point of view) for the last millennium. Here are major sources for the political, religious, and social history of the countries of Europe. It should not be thought that the information here contained is restricted only to matters of political and diplomatic interest, to foreign affairs and religious disputes. There is in fact a wealth of material on social subjects and ordinary people, on education, on hospitals, on marriage, divorce, illegitimacy, on occupations and industries, on violence, excommunication, and heresy.

The story of the opening of the papal ‘Archivio Segreto’ in 1883 has already been robustly told by Owen Chadwick. It had much to do with the events of the previous seventy years: the transport of the papal archives to Paris by Napoleon in 1810–11 and the more recent event of the calling of the Vatican Council in 1870. Such secret archives and sensitive papers as those concerning the trial of Galileo and the Trial of the Templars disappeared in Paris at this time, and were only recovered in part. The minutes of the sixteenth-century Council of Trent survived and were duly returned with the rest, but the sojourn of the archives in Paris had opened up sensitive papers to public, and possibly hostile, gaze. When the Vatican Council was called in 1870, the procedure of the great Council of Trent was examined and found to be much more liberal than that proposed. The archivist was accused of leaking this information and consequently his entrance to the Archives was walled up. The Secret Archives remained exactly that, secret to all but a very few.