[21] In Clery’s “Minor Tactics” occurs the following astonishing passage: “The use made of entrenchments by the Turks was not the least remarkable feature of the war of 1877. Field works, as aids in defense, had been used with advantage in previous wars, but no similar instance exists of an impregnable system of earthworks being improvised under the very noses of the enemy.” Col. Clery’s book is an evidence of his intelligent study and thorough knowledge of European military history; yet, as late as 1885, this professor of tactics at the Royal Military College at Sandhurst seems not to have heard of Johnston’s works at Kenesaw Mountain, or the fortifications constructed at Spottsylvania and Petersburg. [22] May’s “Tactical Retrospect.” [23] For a description of the American military telegraph, see Grant’s Memoirs, Vol. II., p. 205, _et seq._ See also the comments on the military telegraph, in Sherman’s Memoirs, Vol. II., p. 398. APPENDIX I. THE PRUSSIAN ADVANCE FROM KÖNIGGRÄTZ TO THE DANUBE. The day after the battle of Königgrätz was occupied by the Prussians in resting their fatigued troops, and in separating the mingled corps and detachments of the different armies. Late in the afternoon the first movements in advance began. The fortresses of Josephstadt and Königgrätz were still in the hands of the Austrians. They were well garrisoned, and could only be taken by siege. Both were summoned to surrender, and both refused. These fortresses were of the greatest importance, as they commanded the line of railway on which the Prussians depended for supplies, and controlled the passage of the Elbe in the vicinity of the battle field. Strong detachments were, therefore, left to mask the fortresses, and on the 5th of July the Prussian armies marched to Pardubitz and Przelautsch, at which points they crossed the Elbe. A division of Landwehr was sent to Prague, which city surrendered, without resistance, on the 8th of July. The Prussians were thus able to open communications with the rear by rail, _via_ Pardubitz, Prague, Turnau and Reichenberg, in spite of the fortresses of Theresienstadt, Königgrätz and Josephstadt. After the battle of Königgrätz all touch with the Austrians had been lost, and for three days the Prussians were completely in the dark as to the direction taken by the retreating army. On July 6th it was learned that Von Benedek, with the greater portion of his army, had retreated upon Olmütz.