Abstract
Asturian, Galician as well as some dialects of Northeast Portuguese characteristically present the root fa- in the 2sg, 3sg and 3pl of the present of indicative and in the 2sg of the imperative of the verb facer/fazer/faer/fer. These forms also appear in the same persons of the present of indicative of Aragonese and Catalan (although not in the 2sg of their Imperative). This paper takes the stance that all these forms have a common origin in an Italo-Gallic variety of vulgar Latin. To explain their dispersion in the verbal paradigm, the notion of morphome is used. The contribution shows how history (in this case, linguistic and geographical contact) can help us to identify a possible diachronic explanation.