French troops returned to Italy in 1799, following a brief period of absence which had precipitated the collapse of their Italian client republics. Napoleon Bonaparte, who had seized power in the Coup of 18 Brumaire, carried out a crossing of the Alps with his Army of the Reserve (officially commanded by Louis-Alexandre Berthier) in May 1800. This move, made almost before the passes were open, threatened Austrian General Michael von Melas' lines of communications in northern Italy. The French army then seized Milan on 2 June, followed by Pavia, Piacenza and Stradella, cutting the main Austrian supply route eastward along the south bank of the Po river. Bonaparte hoped that Melas' preoccupation with the Siege of Genoa, held by French General André Masséna, would prevent the Austrians from responding to his offensive. However, Masséna surrendered the town on 4 June, freeing a large number of Austrians for operations against the French.