Definition of "échelon"

As soon as the infantry had replenished their ammunition, they wheeled to the left in échelon of brigades, and began to march towards Surgham ridge. The movements of a great force are slow. It was not desirable that the British division, which led the échelon, should remain in the low ground north of Surgham—where it was commanded, had no field of fire, and could see nothing—and accordingly both these brigades moved forward almost together to occupy the crest of the ridge.

1899, Winston Spencer Churchill, “The Battle of Omdurman: September 2, 1898”, in F[rancis] Rhodes, editor, The River War: An Historical Account of the Reconquest of the Soudan [...] In Two Volumes, volume II, London: Longmans, Green, and Co., 89 Paternoster Row, pages 145–146