When Marlborough took command of the allied armies in the Netherlands in 1702, it was clear to him, that the danger to the cause of the allies generally lay in the isolation of Austria. Cut off from the sea, she could not be directly assisted by the English and Dutch fleets. Accessible from Italy through the passes of Tirol, she might easily be taken in flank should she receive a repulse in that quarter. On the side of the Rhine the danger was not only threatening, but imminent. Bavaria was about to make common cause with Louis, and a united French and Bavarian force might be at the gates of Vienna long before tardy succours could force their way there from north Germany or the Netherlands. It was therefore all-important to Marlborough to gain command of the lower Rhine valley, so as to be able to open up communications with the imperial troops on the upper Rhine or upper Danube if necessary. But in the way of this policy there were considerable difficulties. The Netherlands formed one vast intrenched camp in the hands of the French. Behind the curtain of their fortresses they could make their preparations in secret for a sudden advance upon Amsterdam, or recruit their armies after a repulse. Boufflers at the head of the French forces occupied a line which stretched from Antwerp on the Scheldt, through Venlo on the Meuse, to Kaiserwerth on the Rhine, thus blocking the three river valleys. If driven from that by a front attack, he had but to retire on the line of the Demer, between Antwerp and Liége, or a little further back to the line of the Mehaigne from Antwerp through Louvain and Tirlemont to Namur, or further back still to the line of the frontier, and take refuge under the great fortresses of Lille, Tournai, Mons, Charleroi and Namur. To force these positions one after another, and capture the fortresses which defended them, in the face of a watchful and valiant enemy, was a task of much difficulty, and must take many years. [Sidenote: =Marlborough gains a footing on the Rhine, 1702.=] To try and turn the fortresses by advancing on France by the valleys of the Rhine and the Moselle was sure to be bitterly opposed by the Dutch, whose timidity already pictured the French at the gates of Amsterdam. Marlborough had therefore to act very cautiously. He took advantage of Boufflers’s too extended position, and directed an attack as if to turn his left in Brabant. Boufflers fell into the trap, moved his troops in all haste to defend his left, and so gave his right flank over into the enemies’ hands. Marlborough easily turned his right flank between the Meuse and the Rhine, drove him back on the line of the Mehaigne, and established himself strongly on the valleys of the Meuse and the Rhine, capturing Venlo, Ruremonde, and Liége. [Sidenote: =His indecisive campaign of 1703.=]