General Frossard's II Corps and Marshal Bazaine's III Corps crossed the German border on 2 August, and began to force the Prussian 40th Regiment of the 16th Infantry Division from the town of Saarbrücken with a series of direct attacks. The Chassepot rifle proved its worth against the Dreyse rifle, with French riflemen regularly outdistancing their Prussian counterparts in the skirmishing around Saarbrücken. However the Prussians resisted strongly, and the French suffered 86 casualties to the Prussian 83 casualties. Saarbrücken also proved to be a major obstacle in terms of logistics. Only one railway there led to the German hinterland but could be easily defended by a single force, and the only river systems in the region ran along the border instead of inland. While the French hailed the invasion as the first step towards the Rhineland and later Berlin, General Le Bœuf and Napoleon III were receiving alarming reports from foreign news sources of Prussian and Bavarian armies massing to the southeast in addition to the forces to the north and northeast.

On which date did Frossard's and Bazaines's troops cross the German border?