On the basis of a discussion of the structural expansion of the Aragonese Crown’s feudal system over Sharq al-Andalus during the 12th and 13th centuries, which was similar to that occurred in other European countries at the time, this paper offers an assessment of the contribution of Aragonese immigrants to the repopulation of the País Valencià during the 13th century. After explaining the different quantitative weight of Aragonese colonists in the various Valencian areas, with very little presence in the north of Castelló, a review is made of Aragonese society in the 12th century, focusing on those traits having an influence on the linguistic levelling process with their contemporary Catalan colonists in Valencian areas. Emphasis is made on the linguistic duality between Aragonese and Spanish in the Aragonese kingdom in the 12th and 13th centuries and on the different demographics, with greater population density north of the river Ebro. This leads us to describe Aragonese society as a dual one, having a different numerical contribution to language contact in the creation of Valencian society of the low Middle Ages.