Gallaecia or Callaecia was the name of a Roman province that comprised a territory in the north-west of Hispania (approximately present-day Galicia in Spain, northern Portugal, León (province) and Asturias). The most important city and historical capital of Callaecia was the town of Bracara Augusta, the modern Portuguese Braga.
The Romans gave the name Gallaecia to the northwest part of the Iberian peninsula after the Gallaeci (Greek Kallaikoi) tribe (or Gallaecians). These Gallaeci lived in the Douro Valley with center in Cale in the area that would become the Roman town of Portus Calle, today's Porto. However it is not sure that there was a specific tribe called Callaeci, because the main people between Douro and Lima rivers were the Bracari.
Gallaecia, as a region, was thus marked for the Romans as much for its Celtic culture, the culture of the castros or castreja — hillforts of Celtic origin—as it was for the lure of its gold mines. This civilization extended over present day Galicia, the north of Portugal, the western part of Asturias, the Berço, and Sanabria.
At a far later date, the mythic history that was encapsulated in Lebor Gabála Érenn credited Gallaecia as the point from which the Celts sailed to conquer Ireland, as they had Gallaecia, by force of arms.
After the Punic Wars, the Romans turned their attention to conquering Hispania. The tribe of the Gallaicoi 60,000 strong, according to Paulus Orosius, faced the Roman forces in 137 BC in a battle at the river Douro (Duero, Douro, Durius), which resulted in a great Roman victory, by virtue of which the Roman proconsul Decimus Junius Brutus returned a hero, receiving the agnomen Gallaicus ("conqueror of the Gallaicoi"). From this time, Gallaecian fighters joined the Roman legions, to serve as far away as Dacia and Britain. The final extinction of Celtic resistance was the aim of the violent and ruthless Cantabrian Wars fought under the emperor Octavian from 26 to 19 BC. The resistance was appalling: collective suicide rather than surrender, mothers who killed their children before committing suicide, crucified prisoners of war who sang triumphant hymns, rebellions of captives who killed their guards and returned home from Gaul.
For Rome Gallaecia was a region formed exclusively by two conventus—the Lucensis and the Bracarensis — and was distinguished clearly from other zones like the Asturica, according to written sources:
In the 3rd century, Diocletian created an administrative division which included the conventus of Gallaecia, Asturica and, perhaps, Cluniense. This province took the name of Gallaecia since Gallaecia was the most populous and important zone within the province. In 409, as Roman control collapsed, the Suebi conquests transformed Roman Gallaecia (convents Lucense and Bracarense) into the kingdom of Galicia (the Galliciense Regnum recorded by Hydatius and Gregory of Tours).
In Beatus of Liébana (d. 798), Gallaecia refers to the Christian part of the Iberian peninsula, whereas Hispania refers to the Muslim one. The emirs found it not worth their while to conquer these mountains filled with fighters and lacking oil or wine.
In Charlemagne's time, bishops of Gallaecia attended the Council of Frankfurt in 794. During his residence in Aachen, he received embassies from Alfonso II of Asturias, according to the Frankish chronicles.
Sancho III of Navarre in 1029 refers to Vermudo III as Imperator domus Vermudus in Gallaecia.
Gene flow and genetic structure in the Galician population (NW Spain) according to Alu insertions.(Research article)(Clinical report)
Dec 02, 2008; Authors: Tito A Varela (corresponding author) ; José Fariña ; Lois Pérez Diéguez ; Rosa Lodeiro  Background Alu...