The news of the taking of Caporetto on the morning of October 24 had about as startling an effect at Italian headquarters as would be produced on the British front if it were suddenly announced that the Germans were in Ypres. Not only was Caporetto a town on the Upper Isonzo which the Italians had seized by dashing forward across the frontier the very morning that war was declared, but it also stood at the head of a most important strategical valley leading back into the mountains on which the Italian main line lay, and from the town lead several easy roads that follow various routes into the plain beyond. Already the enemy was pressing in force along those roads. The Italians had, indeed, fallen back to reserve positions, but were the enemy to win through--as he did within two days--he would be on the flank and almost in the rear of the whole Italian Army of a million men. [Sidenote: Rapid progress of the Germans is difficult to explain.] [Sidenote: Italian outposts are surrounded.] Just how the Germans progressed so fast that by noon on October 24 they had a machine-gun posted on the square in Caporetto still remains, eight days later, incompletely explained. All that is really known is this: at 2 a.m. they started a very violent bombardment. When the shelling suddenly stopped after only two hours, the Italians regarded the interruption merely as a lull, for the artillery preparation for an infantry attack in force usually lasts much longer. With the valley hidden by darkness, mist, and rain, and seeing more dimly than usual through the mica of their gas-masks, the Italians knew nothing of the German infantry's advance up the valley from the Santa Lucia bridgehead, south of Tolmino, until the enemy had actually reached their wire. In this way the Plec line of defense across that reach of the Isonzo known as the Conca di Plezzo, a line specially designed to check an offensive from Santa Lucia, was captured by surprise, and then German troops poured down into the river gorge from Mrzli on its eastern side, until the valley was full of the enemy, and Monte Nero and the other Italian outpost positions on the heights beyond the Isonzo were completely surrounded. [Sidenote: Violent fighting on the Bainsizza plateau.]