In 1888, the French began to study a possible German offensive north of Verdun or through Belgium and Plan XII was written with a contingency for a German breach of Belgian neutrality. In 1904, this was given more attention after a German ( Avenger) sold a copy of the German concentration plan to French intelligence and described mobilisation methods and war plans. Using this windfall and other sources of information, the French adapted Plan XV of 1906, to be ready for a German invasion of Belgium and later plans contained increases in the forces to be assembled to the north and north-east of Verdun. Plan XVI of March 1909, anticipated a German enveloping manoeuvre through Luxembourg and Belgium, after the findings of a 1908 analysis by General Henri de Lacroix, in which he dwelt on the German preference for enveloping manoeuvres and predicted that two German armies would march through eastern Belgium, around the northern flank of the French fortress zone, one to emerge from the Ardennes at Verdun and the other at Sedan. Lacroix wanted to improve the prospects of the usual defensive-offensive strategy by assembling a new Sixth Army near Châlons-sur-Marne, (now Châlons-en-Champagne), west of Verdun, easily to move towards Toul in the centre, Verdun on the left or to the vicinity of Sedan and Mézières behind the northern flank.