On August 7th Essen made an attack on Schlock, the port at the mouth of the Aa, with 6 British and 13 Russian sloops and gunboats, and about 1000 troops, all under General Lewis. Schlock was taken, but the light craft could not pass the Prussian batteries on the Aa, and Lewis abandoned Schlock and withdrew. Oudinot, after his fruitless attack on the bridge-head of Dünaburg on July 13th, moved up the left bank of the Düna to join in the general advance on Vitebsk. He also endeavoured to render the works at Drissa indefensible. Wittgenstein, realising that Macdonald and Oudinot could not easily combine their operations, at first resolved to attack the 2nd Corps as it passed up the Düna; but on receiving a report that Macdonald was bridging the river at Jakobstädt he took up a position near Razitzi (? Pazitzi), about 16 miles from Druia on the road to Sebezh, and awaited events. Oudinot, moving up the left bank of the Düna, left Merle’s division, chiefly Swiss, and Corbineau’s brigade of light cavalry to watch the river about Drissa, and with the rest of the 2nd Corps and Doumerc’s Cuirassier division, occupied Polotsk on the 26th. On the 28th, leaving a battalion at Polotsk, he advanced on Sebezh to cut Wittgenstein’s communications with St. Petersburg. He crossed the Drissa at Sivokhino and, early on the 30th, reached the hamlet of Kliastitzi, some 34 miles from Sebezh. As he was very badly informed as to Wittgenstein’s movements he decided to halt and send out reconnaissances. Meanwhile Wittgenstein, informed of Oudinot’s advance, had determined to attack without delay. On the 30th he was within easy reach of Oudinot’s left flank; and about four in the afternoon his advance-guard came into contact with Legrand’s division at Jakubovo, about 2 miles west of Kliastitzi, posted on a narrow front between two woods. Wittgenstein had with him the whole 1st Corps and 6 depôt battalions, in all about 21,000 men and 96 guns, organised into a vanguard, under Kulnev, 2 infantry divisions under Major-Generals Berg and Sazonov, and a mixed division commanded by Major-General Kakhovski.