To guard against the attacks made on the railway lines in the Orange Free State and the Transvaal during the British occupation, entrenched posts were placed at every bridge exceeding a 30-feet span; constant patrolling was maintained between these posts; and the block-houses introduced (in 1901) by Lord Kitchener were erected along all the railway lines, at distances of about 2,000 yards. Each block-house, also, was garrisoned by about ten men, and each was surrounded by wire entanglements which, together with various kinds of alarm fences, were also placed between the block-houses themselves in order both to impede the approach of the enemy and to warn the garrison thereof. _Block-houses_ are to-day regarded as one of the chief means of protecting railways against attacks. Their construction and equipment are dealt with by Major W. D. Connor, of the Corps of Engineers, U.S.A., in "Military Railways" (Professional Papers, No. 32, Corps of Engineers, U.S. Army, Washington, 1910). Supplementary to the adoption of this block-house system, in time of war, is the practice followed in various Continental countries, in time of peace, of building _permanent fortresses_, in solid masonry, alongside railway bridges crossing important rivers. In some instances the fortress is so constructed that the railway lines pass through the centre of it. Not only, as a rule, are these fortresses extremely solid and substantial, but they may be provided with bomb-proof covers and be stocked with a sufficient supply of provisions to be able to stand, if necessary, a fairly prolonged siege. One can assume, also, that the garrison would have under its control facilities arranged in advance for the destruction of the bridge, as a last resort, in case of need. The theory is that such fortresses and their garrisons should be of especial advantage, on the outbreak of war, in checking any sudden invasion and allowing time for the completion of defensive measures. Their construction in connection with all the principal railway bridges crossing the Rhine was especially favoured in Prussia after the war of 1870-1. Similar fortresses, or "interrupting forts," as the Germans call them, are also built for the protection of important tunnels, junctions, locomotive and carriage works, etc. Another method adopted for the safeguarding of railway lines in war is the use of _armoured trains_; though in practice these are also employed for the purposes of independent attacks on the enemy, apart altogether from any question of ensuring the safety of rail communication.[10] For the _protection of locomotives and rolling stock_, and to prevent not only their capture but their use by the enemy, the most efficacious method to adopt is, of course, that of removing them to some locality where the enemy is not likely to come.