By adroit moves on the borders of the lake, Bonaparte now sought to make Beaulieu nervous about his communications with Tyrol through the river valley of the Adige; he completely succeeded: seeking to guard the important positions on that river between Rivoli and Roveredo, Beaulieu so weakened his forces on the Mincio, that at Borghetto and Valeggio he had only two battalions and ten squadrons of horse, or about two thousand men. Lannes' grenadiers, therefore, had little difficulty in forcing a passage on May 30th, whereupon Beaulieu withdrew to the upper Adige, highly satisfied with himself for having victualled the fortress of Mantua so that it could withstand a long siege. This was, practically, his sole achievement in the campaign. Outnumbered, outgeneralled, bankrupt in health as in reputation, he soon resigned his command, but not before he had given signs of "downright dotage."[54] He had, however, achieved immortality: his incapacity threw into brilliant relief the genius of his young antagonist, and therefore appreciably affected the fortunes of Italy and of Europe.
Bonaparte now despatched Masséna's division northwards, to coop up the Austrians in the narrow valley of the upper Adige, while other regiments began to close in on Mantua. The peculiarities of the ground favoured its investment. The semicircular lagoon which guards Mantua on the north, and the marshes on the south side, render an assault very difficult; but they also limit the range of ground over which sorties can be made, thereby lightening the work of the besiegers; and during part of the blockade Napoleon left fewer than five thousand men for this purpose. It was clear, however, that the reduction of Mantua would be a tedious undertaking, such as Bonaparte's daring and enterprising genius could ill brook, and that his cherished design of marching northwards to effect a junction with Moreau on the Danube was impossible. Having only 40,400 men with him at midsummer, he had barely enough to hold the line of the Adige, to blockade Mantua, and to keep open his communications with France.
At the command of the Directory he turned southward against feebler foes. The relations between the Papal States and the French Republic had been hostile since the assassination of the French envoy, Basseville, at Rome, in the early days of 1793; but the Pope, Pius VI., had confined himself to anathemas against the revolutionists and prayers for the success of the First Coalition.