Viriathus (also spelled Viriatus; known as Viriato in Portuguese and Spanish; died 139 BC) was the most important leader of the Lusitanian people that resisted Roman expansion into the regions of western Hispania (as the Romans called it). Viriatus developed alliances with other Iberian groups, even far away from his usual theatres of war, inducing them to rebel against Rome. He led his army, supported by most of the Lusitanian and Vetton tribes as well as by other Celtiberian allies, to several victories over the Romans between 147 BC and 139 BC before being betrayed by them and murdered while sleeping.
Little is known about Viriathus. The only reference to the location of his native tribe was made by the Greek historian Diodorus Siculus, who claims he was from the Lusitanian tribes of the ocean side. Livy described him as a shepherd who became a hunter, then a soldier, thus following the path of most young warriors, the iuventus, who devoted themselves to cattle raiding, hunting and war.
According to Appian, Viriathus was one of the few who escaped when Galba, the Roman governor, massacred the flos iuventutis, the flower of the young Lusitanian warriors, in 150 BC. Two years after the massacre, in 148 BC, Viriathus became the leader of a Lusitanian army.
Viriatus was described as a man who followed the principles of honesty and fair dealing and was acknowledged for being exact and faithful to his word on the treaties and alliances he made. Livy gives him the title of vir duxque magnus with the implied qualities that were nothing more than the ideals of the ancient virtues.
In the 3rd century BC, Rome started its conquest of the Iberian Peninsula. The Roman conquest of Iberia began during the Second Punic War, when the senate sent an army to Iberia to block Carthaginian reinforcements from helping Hannibal in the Italian Peninsula. This began Roman involvement in 250 years of subsequent fighting throughout Iberia, resulting in its eventual conquest in 19 BC with the end of the Cantabrian Wars. The Lusitanian War is one of the most well documented episodes of the conquest.
The Lusitanians revolted first in 194 BC against the Romans. Iberia was divided between the tribes that supported Roman rule and the tribes that revolted against Roman rule, as they had been divided before by those who supported the Carthaginian or the Romans.
Knowing that the Lusitanian resistance was largely due to Viriathus' leadership, Quintus Servilius Caepio bribed Audax, Ditalcus and Minurus, who had been sent by Viriathus as an embassy to establish peace. These ambassadors returned to their camp and killed Viriathus while he was sleeping. Eutropius claims that when Viriathus' assassins asked Q. Servilius Caepio for their payment he answered that "it was never pleasing to the Romans, that a general should be killed by his own soldiers.", or in another version more common in modern Portugal and Spain, "Rome does not pay traitors who kill their chief". Total pacification of Lusitania was only achieved under Augustus. Under Roman rule, Lusitania and its people gradually acquired Roman culture and language.