Bonaparte now determined to hazard one of the most daring turning movements which history records. It was necessary at all costs to drive Alvintzy from the heights of Caldiero before the Tyrolese columns should overpower Vaubois' detachment at Rivoli and debouch in the plains west of Verona. But, as Caldiero could not be taken by a front attack, it must be turned by a flanking movement. To any other general than Bonaparte this would have appeared hopeless; but where others saw nothing but difficulties, his eye discerned a means of safety. South and south-east of those hills lies a vast depression swamped by the flood waters of the Alpon and the Adige. Morasses stretch for some miles west of the village of Arcola, through which runs a road up the eastern bank of the Alpon, crossing that stream at the aforenamed village and leading to the banks of the Adige opposite the village of Ronco; another causeway, diverging from the former a little to the north of Ronco, leads in a north-westerly direction towards Porcil. By advancing from Ronco along these causeways, and by seizing Arcola, Bonaparte designed to outflank the Austrians and tempt them into an arena where the personal prowess of the French veterans would have ample scope, and where numbers would be of secondary importance. Only heads of columns could come into direct contact; and the formidable Austrian cavalry could not display its usual prowess. On these facts Bonaparte counted as a set-off to his slight inferiority in numbers.