 Complete the following phrase:  The barrage was constructed from 1686 to 1690 in pink Vosges sandstone by the French Engineer Jacques Tarade according to plans by Vauban. The principal defensive function of the barrage was to enable, in the event of an attack, the raising the level of the River Ill and thus the flooding of all the lands south of the city, making them impassable to the enemy. This defensive measure was deployed in 1870, when 