exceptional depth also was necessary, as the stage arrangements were to be such as to admit a scene fifty feet high to be lowered on its frame.it was therefore necessary to lay a foundation in a soil soaked with water which should be sufficiently solid to sustain a weight of 22, pounds, and at the same time to be perfectly dry, as the cellars were intended for the storage of scenery and properties.while the work was in progress, the excavation was kept free from water by means of eight pumps, worked by steam power, and in operation, without interruption, day and night, from march second to october thirteenth.the floor of the cellar was covered with a layer of concrete, then with two coats of cement, another layer of concrete and a coat of bitumen.
the wall includes an outer wall built as a coffer-dam, a brick wall, a coat of cement, and a wall proper, a little over a yard thick.
after all this was done the whole was filled with water, in order that the fluid, by penetrating into the most minute interstices, might deposit a sediment which would close them more surely and perfectly than it would be possible to do by hand.twelve years elapsed before the completion of the building, and during that time it was demonstrated that the precautions taken secured absolute impermeability and solidity.
"the events of 1870 interrupted work just as it was about to be prosecuted most vigorously, and the new opera house was put to new and unexpected uses.during the siege, it was converted into a vast military storehouse and filled with a heterogeneous mass of goods.after the siege the building fell into the hands of the commune and the roof was turned into a balloon station.