The episode took place in the spring of 1141, in Vale do Vez, in Arcos de Valdevez , when D. Afonso Henriques , after the victory in the Ourique battle ( 1139 ), broke the Tui's peace ( 1137 ) signed with his cousin the Emperor Alfonso VII of Leon and Castile, and invaded Galicia, conquering some castles under the protectorate of the Leonese monarch. In response, the imperial forces, in much greater numbers, entered Portuguese lands, razing the castles to its passage, descending the mountains of the Soajo towards Valdevez.
After a few hours of skirmishes and provocations, to avoid the pitched battle and save men and resources for the fight against the Arab advance, they were selected the best knights from both sides to fight each other in a I ride or fair, as used in the Middle Ages. The luck of the arms swung to the Portuguese side, with the Leonese knights being detained, according to the code of Medieval cavalry.
This was the decisive episode and the last stage for the birth of Portugal, being the antecedent of the celebration of the Zamora Treaty in 1143 .