Both sides raised special troops during the war. The Liberal side formed the volunteer Basque units known as the Chapelgorris, while Tomás de Zumalacárregui created the special units known as aduaneros. Zumalacárregui also established the unit known as Guías de Navarra from Liberal troops from La Mancha, Valencia, Andalusia and other places who had been taken prisoner at the Battle of Alsasua (1834). After this battle, they had been faced with the choice of joining the Carlist troops or being executed.