This was the celebrated position of Buyak-Tchek-medje, a defensive line twenty-five miles from Constantinople and of remarkable military strength. The peninsula between the Black Sea and the Sea of Marmora is at this point only twenty miles wide, and twelve of these miles are occupied by broad lakes which extend inland from either shore. Of the remaining distance, about half is made up of swamps which are almost or quite impassable, while dense and difficult thickets occupy the rest of the line. Behind this stretch of lake, swamp, and thicket there extends from sea to sea a ridge from four hundred to seven hundred feet in height, the whole forming a most admirable position for defence. This ridge had been fortified by the Turks with redoubts, trenches, and rifle-pits, which, fully garrisoned and mounted with guns, might have proved impregnable to the strongest force. The thirty thousand men within them could have given great trouble to the whole Russian army, and double that number might have completely arrested its march. Yet this great natural stronghold was given up without a blow, signed away with a stroke of the pen. [Illustration: THE WALLS OF CONSTANTINOPLE.] On January 31 an armistice was signed, one of whose terms was that this formidable defensive line should be evacuated by the Turks, who were to retire to an inner line, while the Russians were to occupy a position about ten miles distant. It was no consideration for Turkey that now kept the Russians outside the great capital, but dread of the powers of Europe, which jealously distrusted an increase of the power of Russia, and were bent on saving Turkey from the hands of the czar. On February 12 an event took place that threatened ominous results. The British fleet forced the passage of the Dardanelles and moved upon Constantinople, on the pretence of protecting the lives of British subjects in that city. As soon as news of this movement reached St. Petersburg the emperor telegraphed to the Grand Duke Nicholas, giving him authority to march a part of his army into Constantinople, on the same plea that the British had made. In response the grand duke demanded of the sultan the right to occupy a part of the environs of his capital with Russian soldiers, the negotiations ending with the permission to occupy the village of San Stefano, on the Sea of Marmora, about six miles from the walls of the threatened city.