Contained in two manuscripts preserved in the Biblioteca Apostolica Vaticana is a little-known chronicle by an anonymous writer of the mid-twelfth century which may shed more light on an epoch-making event on the eve of the Crusades: the Norman conquest of Sicily. This source, collated into a single transcription by Giambattista Caruso in 1723 and reproduced in the Rerum Italicarum Scriptores by Ludovico Muratori in 1726, is called the Historia Sicula a Normannis ad Petrum Aragonensem by Anonymus Vaticanus. Despite the fact that it is one of a very few sources to describe a seminal episode in Mediterranean history, the Historia Sicula has not been discussed in any depth for over a century. This essay seeks to correct that oversight.

In his formative work, Mohammed and Charlemagne, the great Belgian historian Henri Pirenne contended that ‘the rapid and unexpected advance of Islam’ had precipitated ‘the end of Mediterranean unity’ by vanquishing the mare nostrum of ancient Rome. The resultant loss of Sicily to the Aghlabids of North Africa in the ninth century established what maritime historian A.R. Lewis termed ‘the Islamic Imperium’ and inspired the fourteenth-century Arab scholar Ibn Khaldūn to claim that ‘the Muslims had gained control over the whole of the Mediterranean’. At the beginning of the eleventh century, the Mediterranean was, in effect, a Muslim lake with most of its major islands, including Sicily, firmly ensconced in Dar al-Islam (the ‘House of Islam’).