Battle of Valmy

On 20 September 1792 on the heights of Valmy in Champagne, Generals Kellermann and Dumouriez halted the Prussian advance of the Duke of Brunswick toward Paris. The 'Cannonade of Valmy,' an hours-long artillery duel, forced the coalition army to abandon its offensive without a decisive pitched battle.

Since the declaration of war in April 1792 the French armies had suffered reverse after reverse and lost their fortresses. An allied army of 150,000 — Prussians, Austrians, Hessians, with 20,000 émigrés — was marching on Paris under the Duke of Brunswick. Dumouriez then carried out a decisive redeployment to hold the passes of the Argonne and establish himself near Sainte-Menehould; Kellermann joined him on 19 September, forming a continuous front across the road to the capital.

On 20 September the engagement was almost entirely an artillery duel, lasting about fourteen hours. The thirty-six French guns, served according to the recently reformed Gribeauval system, fired some twenty thousand rounds and gained the upper hand, while the Prussian columns advanced and fell back without ever closing. The decisive moment was a moral one: Kellermann rallied his shaken troops with 'Comrades, this is the moment of victory', and French resistance broke the Prussian impetus.

Despite his numerical superiority, Brunswick ordered a retreat. Historians still debate why: inadequate logistics, dysentery in the ranks, diplomatic calculations over Poland, or simple misjudgement — he needed a victory in the field to march on Paris without exposing his supply lines. On 21 and 22 September the newly assembled Convention proclaimed the Republic and abolished the monarchy. What was militarily no more than an indecisive cannonade thus became the founding success that legitimised the regime and saved the Revolution.