The Battle of Arras took place on May 9, 1915, during World War One. The so-called Bayonne Legion (a French Foreign Legion infantry unit which consisted of ethnic Polish volunteers) clashed with troops of the Imperial German Army, defending the hill of Vimy, located 10 kilometers north of Arras, France.
In August 1914, after the outbreak of the Great War, several ethnic Poles living in France volunteered to join French Foreign Legion, hoping that a separate, Polish unit would be created within that formation. On August 21, 1914, French authorities agreed to the request of Committee of Polish Volunteers, and soon afterwards, two Polish units were formed. Some volunteers were sent to Bayonne, where a company of some 180 soldiers was formed and trained. This company came to be called the Bayonne Legion, and it became 2nd Company of 1st Foreign Legion Regiment (1st Infantry Division). Its officers were French, while Poles served in lower ranks.
Other volunteers were sent to Rueil, where a second company was formed. On October 22, 1914, the Bayonne Legion was sent to the frontline in Champagne, where they took positions near Sillery, Marne, as part of Moroccan Infantry Division. Until April 1915, the Poles kept their positions along the Aisne river.
On May 9, the Legion attacked the hill of Vimy, located some ten kilometers from Arras. They managed to capture German trenches, but with very heavy losses, reaching 75% of the manpower. Only some 50 soldiers remained alive after the battle, and all officers died, including commandant of the Legion, major Osmonde. As a result of these losses, remnants of the unit were withdrawn to the rear. On June 16 near Souchez, several soldiers died in a clash with German forces, and in the summer of 1915, the company was dissolved. Most of the survivors in 1917 joined the Blue Army.
The Battle of Arras is commemorated on the Tomb of the Unknown Soldier, Warsaw, with the inscription "ARRAS 9 V 1915".