The primitive human presence on where Seia lies today dates back to pre-Roman times, when a settlement was founded by the
Turduli, around the
4th century BC, under the name Senna. The Turduli built a
castro in the place of Nogueira, between the hills of Santana and Carvalha do Outeiro. Three smaller castros strategically defended it, one in São Romão, another in Crestelo and a third in what is now Seia. There are still remains of castros in Travancinha, Loriga and São Romão. When the
Roman invasion of the Iberian Peninsula took place, the
Lusitanians made the mountain range, then called Montes Hermínios, their headquarters, which became a strong hurdle for the invaders. This did not, however, prevent
General Galba from massacring 30,000 Lusitanian mountaineers. When the Romans became lords of the land, they then transformed the Iberian castro of Nogueira into the Roman "Civitas Sena", which was fortified when it became an Ópido with the same name. It was later occupied by the
Visigoths and the
Moors, the latter from the 8th century onwards. At the time of the
Christian Reconquest of the Iberian Peninsula, the town was definitively conquered from the Moors by
Fernando Magno, who rebuilt its fortification. About this episode, the chronicle of monk Silas recounts the violence of the attack and how the Christians forced the occupants of Ópido Sena to flee towards Viseu. During the time of formation of the Portuguese nationality, Bermudo Peres,
Teresa of León's brother-in-law, started a revolt in the castle of Seia. He was unsuccessful, as
Afonso I, having learned of this, went to meet him with his forces and expelled him from the castle. In the following year, he donated the domains of Seia and its castle to his servant João Viegas in recognition of services rendered. A few years later, the sovereign granted the first charter to the village in 1136, designating it Civitatem Senam. Other charters followed, such as the one granted by
Afonso II, in December 1217, that of
Duarte of Portugal, in December 1433, that of
Afonso V, in August 1479, and, finally, that of
Manuel I, on 1 June 1510. It was in Seia that the last republican rally was held before the
establishment of the Portuguese Republic in 1910. This rally took place on the 25th of September and was chaired by
Afonso Costa, a local of Seia. ==Population==