The 2nd Army conducted the withdrawal with the line-holding divisions, which were fresher than the divisions of the 1st Army and assisted by several cavalry divisions and cyclist battalions. On 17 March, withdrawals began north of the Avre and by 18 March, the German 7th, 2nd, 1st and the southern wing of the 6th Army, began to withdraw from the old front-line ( in length, as the crow flies). Soissons was abandoned, roads leading out of Noyon were flooded, railway bridges were blown and the Somme River and canal crossings from Offoy to Péronne were destroyed. Roads built on causeways over marshy ground between the river and canal, caused water to form pools wide, making crossings practical only at the causeways. The bridges over the rivers Germaine, Omignon, Cologne, Tortille and the Canal du Nord were also destroyed and huge craters blown in crossroads, the damage being made worse by the spring thaw. German rear-guards made a stand in part of the from Nurlu to Péronne on 18 March, which was the third and final marching day of the retreat from Roye to St Quentin and the second and final day from Péronne to le Catelet, when the main body of German troops reached the (Hindenburg Line). Work was still being done to remedy defects in the original position and the rear-guards retired next day from Nurlu and Bertincourt as soon as British troops appeared, then counter-attacked British cavalry around Poeuilly on 22 March.