During the lead-up to the Battle of Marengo, the vanguard of the French army in Italy engaged and defeated an Austrian force in a "glorious victory".

General der Kavallerie Michael von Melas held Turin with 18,000 men, FML Peter Ott's 16,000 troops remained near Genoa where they secured the surrender of GD André Masséna's starving garrison on 4 June, and FML Anton von Elsnitz with 8,000 soldiers retreated from the Riviera.

[2] Lannes moved south from Milan with the army's vanguard, seizing Pavia on 3 June and being initially repulsed by Piacenza's tiny 400-man garrison.

These actions placed French forces directly on the main Austrian line of communication between Alessandria and Mantua in the strategic Stradella defile.

Ott directed O'Reilly with six infantry battalions and four cavalry squadrons to defend the village of Casteggio on the main east-west highway.

Believing that his enemies could not be in strength, Napoleon sent a note to Lannes, "If troops should present themselves between Voghera and Stradella let them be attacked without caution; they are, certainly, fewer than 10,000 men.

Watrin aggressively fed his units into the battle, but found his three demi-brigades, two batteries and one cavalry regiment opposed by a superior force.

Despite intense Austrian artillery fire, the combined pressure forced back Ott's tired soldiers and convinced that general to order a phased withdrawal.

"[14] On the other hand, "Austrian morale suffered a serious relapse, and Melas remained as if hypnotized around Alessandria for the next five days without making any significant move, waiting for his troops to complete their concentration.