"Le Boudin" (French pronunciation: [lə budɛ̃]), officially "Marche de la Légion Étrangère" (English "March of the Foreign Legion"), is the official march of the French Foreign Legion. "Le Boudin" is a reference to boudin, a type of blood sausage or black pudding. Le boudin colloquially meant the gear (rolled up in a blanket) that used to be carried atop the backpacks of Legionnaires.
While the tune was composed prior to the Legion's departure for Mexico in the 1860s the lyrics were progressively composed after the Franco-Prussian War, since Alsatians and Lorrains flocked to the legion after these regions were annexed by Germany. The song makes also repeated reference to the fact that the Belgians are "lazy shirkers", this comes from the fact that the King of the Belgians, who wished to remain neutral in the Franco-German conflict, asked the French government to not commit the Belgian Legionnaires into the conflict. France agreed to this request and the Belgian Legionnaires remained in French Algeria (the Legion's home), to the dismay of the rest of the Legionnaires. This is why the song says that there's no blood sausage (boudin) for the Belgians. The song also mentions the Swiss who constituted the most important foreign contingent of the Legion in the 1870s.
The song relates the feat of arms of the Legion in Tuyen Quang (1884-1885) and in Camerone (1863), the date of which (April 30) is celebrated as the Legion's anniversary.
"Le Boudin" is sung while standing to attention or marching by all ranks of the French Foreign Legion. The Legion marches at only 88 steps per minute, much slower than the 120 steps per minute of all other French military units. Consequently, the Legion contingent at the Bastille Day military parade march brings up the rear. Nevertheless, the Legion gets the most enthusiastic response from the crowd.