In August 1792, a large Austro-Prussian army commanded by the Duke of Brunswick crossed the frontier and began its march on Paris with the declared intention of restoring full power to Louis XVI. Several Revolutionary armies were easily defeated by the professional Austrian, Hessian, Brunswick and Prussian troops. The immediate result of this was the storming of the Tuileries Palace by an armed Parisian mob and the overthrow of the king. Successive Revolutionary forces failed to halt Brunswick's advance, and by mid-September it appeared that Paris would fall to the monarchists. The Convention ordered the remaining armies to be combined under the command of Dumouriez and François Christophe Kellermann. At the Battle of Valmy on 20 September 1792, the Revolutionary forces defeated Brunswick's advance guard, causing the invading army to begin retreating to the border. Much of the credit for the victory is owed to the French artillery, widely viewed as the best in Europe thanks to the technical improvements of Jean Baptiste Vaquette de Gribeauval.