It is believed by some scholars that early in the first millennium BC, several waves of Celts invaded Portugal from Central Europe and inter-married with the local populations, forming different tribes. Another theory suggests that Celts inhabited Western Iberia / Portugal well before any large Celtic migrations from Central Europe. In addition, a number of linguists expert in ancient Celtic have presented compelling evidence that the Tartessian language, once spoken in parts of SW Spain and SW Portugal, is at least proto-Celtic in structure. Modern archeology and research shows a Portuguese root to the Celts in Portugal and elsewhere. During that period and until the Roman invasions, the Castro culture (a variation of the Urnfield culture also known as Urnenfelderkultur) was prolific in Portugal and modern Galicia. This culture, together with the surviving elements of the Atlantic megalithic culture and the contributions that come from the more Western Mediterranean cultures, ended up in what has been called the Cultura Castreja or Castro Culture. This designation refers to the characteristic Celtic populations called 'dùn', 'dùin' or 'don' in Gaelic and that the Romans called castrae in their chronicles.