The front line was to be fortified, to enable its defence with small numbers of troops indefinitely; areas captured were to be recovered by counter-attacks. A second trench was to be dug behind the front line, to shelter the trench garrison and to have easy access to the front line, through covered communication trenches. Should counter-attacks fail to recover the front trench, a rearward line was to be connected to the remaining parts of the front line, limiting the loss of ground to a bend () in the line, rather than a breakthrough. The building of the new defences took until the autumn of 1915 and confronted Franco-British offensives with an evolving system of field fortifications, which was able to absorb the increasing power and sophistication of attacks.