[2] The melody is based on a former song of the Spanish military units in the Rif Wars in Northern Morocco in the 1920s.

The Gandesa front and the blowing up of pontoons and bridges are related to the passage of the river in the Battle of the Ebro, also mentioned in ¡Ay Carmela!.

The Spanish Republican combat engineers were capable of repeatedly repairing the bridges and pontoons in order to allow the loyalist troops to cross the river —at least a few hours every day— despite the steady bombings of the Nazi Condor Legion and the Italian Aviazione Legionaria, as well as the intentional flooding by releasing water from dams upstream.

[3] The moros (Moors) mentioned in some verses are the Regulares, the feared Moroccan shock troop units of the Nationalist faction that kept pounding Republican positions for months at the Gandesa frontline.

[4][5] One popular Civil War variant of this song where the lyrics make reference to the Siege of Madrid is known as "Los Emboscados".