The strategical position of Russia was no more sound than the state of her armaments. She occupied a vast salient, the southern flank of which was the Carpathians. They formed a substantial protection, since the passes afforded poor facilities for transporting the mass of artillery on which Germany relied for success in her attack. But the safety of the flank depended upon the integrity of the front, and a successful German drive in Galicia would expose the entire position of the Russian armies in Poland. The two reasons subsequently given for the dismissal of the Grand Duke Nicholas from the supreme command were, firstly, that he had in the autumn advanced too precipitately into Silesia, and secondly, that in the spring he exhausted his strength in trying to pierce the Carpathians and thus left his front on the Dunajec too weak to resist Mackensen's furious onslaught. But it is doubtful whether any strategic correctitude could have saved the Russian armies from the effects of German superior armaments. The Germans were playing for high stakes, nothing less than the destruction of Russia's offensive capacity; but they were justified in their game by the cards they held in their hand. The attack began on 28 April with a forward move on Dmitrieff's left at Gorlice. The pressure compelled him to weaken his centre along the Biala in front of Ciezkowice. Then on 1 May Mackensen's vast volume of fire burst forth; over 700,000 shells are said to have fallen upon the Russian position, and their defences were blown out of existence. Under cover of this fire, to which the Russians could make little reply, the Biala was crossed, Ciezkowice and Gorlice were captured, and Dmitrieff's line was broken; on the 2nd his army was in full retreat to the Wisloka, twenty miles back in his rear, where no trenches had been dug, and there was little hope of checking the Germans. Nevertheless a heroic stand was here made for five days by Caucasian and other reinforcements. On the 7th Mackensen forced a crossing at Jaslo, and next day he pursued his advantage by seizing two bridgeheads across the Wistok farther on, one at Fryslak to the north and the other at Rymanow to the south. Brussilov's army along the Carpathian foothills at Dukla had to beat a precipitate retreat and lost heavily; it was nearly severed from Dmitrieff's centre. But a counterattack from Sanok in the south and a stand by the Russians at Dembica towards the north procured a slight respite, and by the 14th the bulk of the Russian armies were across the San with their right at Jaroslav, their left at Kosziowa, their centre at Przemysl, and their forces in Poland conforming to the retirement.