ABSTRACT Hundreds of combatants and civilians, both Lao and Vietnamese, perished in the small border town of Thakhek in central Laos on March 21, 1946, when French forces launched their biggest military operation in Indochina at the time. The French victory over the revolutionary forces that day paved the way for the colonial reconquest of Laos and energized France’s military campaign for the reoccupation of Indochina, yet it is barely mentioned in the historiography of the First Indochina War (1945-1954). Drawing on French archives, Lao and Vietnamese documents, and interviews with survivors, this article reconstitutes the history of this massacre and suggests that the massacre has not been fully investigated by historians for two reasons. First, the story of the killing of these hundreds of people – mostly ethnic Vietnamese residing in Laos – sits uneasily between studies of the contemporary history of Laos and academic work on the war between France and the Democratic Republic of Vietnam, thus falling into a historiographical gap. Second, the battle was marked by compromise and miscalculation, which has prevented it from attaining the status of a great anti-colonial battle in the history of the struggle for Lao and Vietnamese independence.