So that our men might cross the countless canals, streams and ditches met with everywhere, and move over flooded and marshy areas, the Belgian engineers built hundreds of bridges and thousands of culverts, besides some tens of kilometres of the foot-bridges already described. As an example, we may mention that one of these foot-bridges, crossing a marsh in the southern part of the front, is quite 800 metres long. As for the road-system, existing roads had to be remade and improved, while new ones were built and narrow ones widened and strengthened sufficiently to carry all kinds of traffic. This road-building and mending was applied to 400 _kilometres of roads and usable tracks_ in all; and absorbed some 500,000 tons of road metal and as many tons of sand--which involved the moving and handling of, say, 1,000,000,000 tons of various materials. The upkeep of the roads, which carry a dense and continuous traffic, demands unceasing labour, especially in the winter. In conclusion, we should mention that there are, in addition to the road-system properly so-called, many infantry routes and approaches for artillery which have had to be made with great difficulty across marshes and soft meadowland. 3. _Various Forms of Construction._--One cannot pretend to give even a bare list of the varied and numberless erections for which our engineers have been responsible behind the Belgian front, to accommodate the fighting troops and auxiliary services and mitigate the scarcity of suitable quarters. For three years German guns have battered everything within range, and converted the humble, peaceful villages of Veurne-Ambacht into heaps of ruins. One must go far behind the front to find any premises that have still escaped shell-fire. In them have been established all the organisations which need not be actually in the lines, and there also are quartered as large a part as possible of the resting units. But they cannot hold all the troops not in the trenches; and it will readily be understood that battalions held in reserve and warned first in case of an attack, must be near enough to throw themselves into the fight without loss of time. The problem has been solved by building a large number of huts in each divisional sector; yet without grouping them so closely as to afford an easy mark to the enemy's guns and aeroplanes. So the hutments, capable of accommodating some 100,000 men and about 15,000 horses, have been scattered over the whole of the district occupied. In addition, much has had to be done and many buildings have had to be erected, in order to secure the best possible conditions for the elaborate organisations of the medical service, even in the fighting zone. We have had to provide bombproof first-aid stations, dressing-stations, and field hospitals, in many cases quite close to the lines, under circumstances the difficulties of which have already been sufficiently emphasised.