We have remarked in passing that much detail work of widely different kinds has had to go forward simultaneously with the organisation proper of the defensive positions. Its execution was entrusted to special troops; engineers (sappers), bridge-builders, telegraphists, railway corps, etc., as well as to many labour companies consisting of men of the older classes attached to the engineers. Men of the heavy and field artillery have had to make the many emplacements for batteries of all calibres, which have increased steadily in number as the Belgian Army has been able to get and assemble in its workshops an abundance of the requisite material. It is impossible to describe the innumerable works of this kind in detail without straying too far, so we will content ourselves here with reviewing them briefly and giving some figures which will enable the reader to appreciate the great responsibilities assumed by the various branches. 1. _Concrete Shelters, Redoubts and Fighting-Posts._--The weakness of earthworks constructed with sand-bags, which are scattered in all directions by bursting shells, has compelled us to build numerous concrete shelters, though the work is beset by many difficulties and sometimes has to be executed right under the enemy's nose--bombproofs, machine-gun posts and fighting-posts for the battalion, regimental and battery staffs. All construction of this kind must be preceded by a thorough consolidation of the ground, which in its natural condition is too soft to support such heavy weights. At several points in the front lines themselves we have also had to make particularly strong _points d'appui_, usually concrete redoubts, in which a large garrison may hold out to the last man. The importance of these works will be inferred from the statement that their construction has involved the use of at least 300,000 to 400,000 cubic yards of concrete. 2. _Communications._--It will be remembered that the district occupied by the Belgian Army was poorly supplied with railways, roads and usable tracks. After the battle of Flanders (October to November, 1914) the continuous movement of troops over the existing roads, added to the effects of bombardment and bad weather, had done great damage to almost all the few available means of communication. This state of things had to be promptly remedied, both to accelerate putting the sector into a state of defence and, what was still more urgent, to enable all kinds of supplies required by the troops and the materials for the defence works to be brought up. Special units, therefore, laid in the advanced army zone some 180 kilometres of new railways of standard gauge, and several hundred kilometres of Decauville railway. The light tracks were gradually pushed through the communication and main trenches, and even along the foot-bridges leading to the main pickets.