Towards the close of March 1917 Arras awoke to an amazing change. Its streets and lanes were once more full of life, and the Roman arch of the Baudimont Gate saw an endless procession of troops and transport. A city makes a difficult base for a great attack. It must be the route of advancing infantry and their billeting area, and it is a mark which the enemy guns can scarcely miss. To minimise this danger the British generals had recourse to a bold plan. They resolved in this section to assemble their armies underground. After the fashion of old French towns, Arras had huge ancient sewers, like those of Paris which may be read of in _Les Misérables_. A map of them was found, and the underground labyrinth was explored and enlarged. Moreover, the town had grown over the quarries from which the older part of it had been built, and these also were discovered. The result was that a second city was created below the first, where three divisions could be assembled in perfect security. The caverns were lit by electricity, plans and sign-posts were put up as if it had been a Tube railway, and a dressing station with 700 beds was constructed. Here it was arranged that the greater part of the VI. Corps should assemble for the attack due east of the city. As a matter of fact the thing was not needed. The Germans shelled the town intermittently, but there was no real bombardment, and before Arras could be methodically destroyed the enemy had been pushed many miles eastward. [Sidenote: _April 5._]