From June–July 1378 the armies of Castile, commanded by John of Trastámara, invaded Navarre and laid the country waste. Charles II retreated over the Pyrenees to Saint-Jean-Pied-de-Port and in October he made his way to Bordeaux to plead for military aid from Sir John Neville, the Lieutenant of Gascony. Neville despatched a small force to Navarre under the knight Sir Thomas Trivet, but the English achieved little over the winter and in February Henry of Trastámara announced his son would re-invade Navarre in the spring. Having no options or allies left Charles II asked for a truce, and by the Treaty of Briones on 31 March 1379 agreed to Henry's demands that he agree to be bound in perpetual military alliance with Castile and France against the English, and to surrender 20 fortresses of southern Navarre, including the city of Tudela to Castilian garrisons.