The Gallo-italic languages arrived in Sicily between 1100 and 1300. They were accompanied by some migrations from Lombardy, Liguria and Monferrato during the Norman domination. The conquerors encouraged the migration towards the island for two reasons: to repopulate some areas where the population had been reduced by epidemics and famines and, on the other hand, to counteract the Arab presence, which was still very important especially in the inland areas such as Enna. The greatest north-south migration occurred during the reign of Roger I, in the second half of the 12th century. Great Count Roger I married Adelaide Aleramici, who was native of northern Italy, fostering the movement of populations from northern Italy to Sicily. Some historical sources certify the Lombard presence some years earlier through the settlement of some mercenaries on the island.

We can assume that the preservation of the Gallo-italic languages was useful to maintain some social needs of the northern population. It was functional for several productive sectors that were carried out by populations belonging to the Norman territories. The Normans considered their knowledge of shipbuilding and the search for raw materials as fundamental. Thus, enclaves were created which allowed the maintenance of the Lombard language. 

This language didn’t follow the same linguistic evolution as that of the countries of origin, so it maintained some characteristics of the Lombard language of the twelfth century, adding some linguistic influences of the local Sicilian languages and some cultural influences of the dominations in the island. In the inland areas of Sicily, this language is now better preserved and has been used over the years in various literary productions. This was particularly the case in the second half of the nineteenth century in the linguistic minority of the province of Enna. In other areas, the linguistic minorities haven’t really become linguistic islands, because the influence of the Sicilian dialect has been stronger.

Reference:
Giacomarra M.G et al. Il trattamento dell'identità in due minoranze storiche di Sicilia in Demiraj B., Mandalà M., Sinani S. (a cura di), Studime Ne te prof. Francesco Altimarit me rastin e60-vjetorit te lindjes/Studi in onore del prof. Francesco Altimari in occasione del 60° compleanno, Edhe 100, 2015. p. 227-250
Ruffino G., Sicilia, collana Profili linguistici delle regioni di Sobrero A.A. (a cura di), Editori Laterza, Bari, 2001
Ruffino G., Introduzione allo studio della Sicilia linguistica, collana Lingue e culture in Sicilia. Piccola biblioteca della scuola di Amenta L., Castiglione M., Valenti I. (a cura di), Centro di studi filologici e linguistici siciliani, 2018
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