Since the Neolithic period, some degree of variance across the island's regions is also attested. The Arzachena culture, for instance, suggests a link between the northernmost Sardinian region (Gallura) and southern Corsica that finds further confirmation in the Naturalis Historia by Pliny the Elder. There are also some stylistic differences across Northern and Southern Nuragic Sardinia, which may indicate the existence of two other tribal groups (Balares and Ilienses) mentioned by the same Roman author. According to the archeologist Giovanni Ugas, these tribes may have in fact played a role in shaping the current regional linguistic differences of the island.