The siege of Fort Bard (21 May-2 June 1800) saw a small Austrian garrison hold up the passage of Napoleon's artillery during the French advance into Italy at the start of the campaign that ended at Marengo. The main part of Napoleon's Army of the Reserve crossed over the Great St. Bernard Pass, while his artillery used the Little St. Bernard. On 16 May Lannes, with the advance guard, reached the top of the pass, and on the next two days pushed the Austrians out of Aosta (17 May) and then Châtillon (18 May). By now he had two infantry divisions and a cavalry brigade under his command, and with this force advanced down the Doire Baltèe valley.
The next obstacle on the French route was Fort Bard. At Bard the valley was almost blocked by Mount Albaredo. The fort was built on an outcrop of the mountain. It had an elliptical plan, which conformed to the shape of the rock, and its gun batteries were well protected from fire from the mountain above. The guns of the fort dominated the village of Bard, which was stretched out along a single street at the base of the rock. The fort was protected by a battalion from Infantry Regiment 47, under the command of Hauptmann Bärnkopf. The French had been aware of the existence of the fort, but hadn't realised how big an obstacle it was.
Lannes soon discovered an alternative route around the fort, using a mule track described by Berthier as linking Armaz to Perlo (probably Arnad to Perloz). This was suitable for infantry, and was soon made usable by cavalry, but was too rough for the artillery. The first French assault, on 21-22 May, was repulsed. Napoleon then reached Bard, and ordered another assault on the fort. This too failed (25 or 26 May), although the village did fall into French hands. On the night of 25-26 May, taking advantage of a storm, the French were able to move six guns past the fort, and others may have followed later, but most of Napoleon's artillery was stuck until the fort fell. Lannes had passed by earliest with the advance guard, capturing Ivrea on 24 May (22 May in some sources).
The main army was not so restricted, and by 26 May the bulk of the infantry and cavalry had bypassed Bard. Chabran's division was left behind to conduct the siege. Gun batteries were in place by 28 May, when a regular bombardment began. By 2 June the French had created a breach in the walls, and this finally convinced Bärnkopf to surrender. The bulk of the French artillery was now free to move past Bard.