After his defeat at Laon on 9-10 March Napoleon was able to retreat to Soissons because of the inertia of General August von Gneisenau, who took command of the Army of Silesia after Prince Gebhardt von Blücher, its commander, was taken ill.
Napoleon remained at Soissons until he learnt that General Emmanuel de St Priest’s corps had moved to Rheims, within striking distance of Soissons, on 12 March. St Priest had been positioned at St Dizier in order to link the Army of Silesia with Prince Karl Phillip zu Schwarzenberg’s Army of Bohemia.
Defeating St Priest would break the Coalition communications and threaten the Army of Silesia’s left rear and the Army of Bohemia’s right flank. Napoleon had been reinforced to 40,000 men since Laon, whilst St Priest had 12,000, a mixture of Russians and conscript Prussian Landwehr.
Napoleon moved rapidly to Rheims, and launched a surprise attack on 13 March. St Priest’s Prussian Landwehr had dispersed to forage for food, and were easily beaten. The Russians put up sterner resistance, but were overwhelmed. The French inflicted 6,000 casualties and suffered only 700. St Priest was amongst the wounded , and died on 29 March. This victory boosted French confidence and caused both Coalition armies to halt their advances.
 Troop strengths are from D. C. B. Lieven, Russia against Napoleon: The Battle for Europe, 1807 to 1814 (London: Penguin, 2010), p. 503.
 Casualties are from D. Chandler, The Campaigns of Napoleon (London: Weidenfeld & Nicolson, 1966), p. 993.