A dialect continuum or dialect chain is a spread of language varieties spoken across some geographical area such that neighbouring varieties differ only slightly, but the differences accumulate over distance so that widely separated varieties are not mutually intelligible.
A variety of languages are spoken as you move from Rome to Northern Italy and then west towards Portugal: Romanesco, Umbrian, Tuscan, Ligurian, Piedmontese, Provençal, Catalan, Castilian Spanish, Galician, Portuguese and several others not mentioned here. Would a certain sequence of these (or other) languages be an example of dialect continuum in Europe?
Focusing [...] on the local Romance lects that pre-existed the establishment of national or regional standard languages, all evidence and principles point to Romania continua as having been, and to varying extents in some areas still being, what Charles Hockett called an L-complex, i.e. an unbroken chain of local differentiation such that, in principle and with appropriate caveats, intelligibility (due to sharing of features) attenuates with distance.