There is a doubt where the first settlements took place. The geographer Plinius stated that opposite the Cies Islands there was an oppidum ( a fortified place) called Abobriga although Abóbriga and Adobriga are also used. This settlement belonged to the Iron-age settlement culture, called like that as the inhabitants lived in fortified sites making the most of the geographical accidents as low hills, peninsulas,... which made easier their defense. However it is rash to identify the oppidum of Abóbriga with the present Baiona, as there are no archaeological evidences to confirm it.
In Roman times, Baiona is known as Erizana, where it is said that in front of the fortified walls of Erizana the Lusitanian leader Viriatus gained a victory against the Romans. Today, we know that the first Roman expeditions which arrived in Galicia in 137 bC., came with the intention of sacking the southern settlements, as they did in Lusitania and the Meseta. Later, there are fewer Roman arrivals, so that the colonization becomes weaker; an evidence of this is the finding of coins, mosaics, arms and vestiges of a Roman road which could be 'Loca Maritima' going along the 'Rias Baixas'(low estuaries). This age is characterized by the survival of the Iron Age culture together with the Roman influence. So , we find the 'villae', rural villas with large estates which were devoted to agricultural expoitations with tenant farmers and slaves.