At the spot selected for the establishment of the viaduct the gauge is deep and steep.  The line passes at 300 feet above the river, and the total length of the metallic superstructure had to be 822 feet.  To support this there was built upon the right bank a pier 158 feet in height, and, upon the left, another one of 196 feet.  The superstructure had been completed, and a portion of it had already been swung into position, when a violent, gale occurred and blew it to the bottom of the gorge.  At the time of the accident the superstructure projected 174 feet beyond the pier on the right bank, and had to advance but 121 feet to reach the 33 foot scaffolding that had been established upon the other pier.

It blows often and violently in this region.  For example, a gale on the 20th of February, 1879, caused great damage, and, among other things, blew the rear cars of a hay train from the top of the Louvoux viaduct to the Bouble.

The superstructure of the Tardes viaduct had already withstood the tempest of the 23d and the 24th of January, 1884, and neither any alteration in its direction nor any change in the parts that held it upon the pile could be perceived.  But on the night of January 26-27 the storm doubled in violence, and the work was precipitated into the ravine.  No one was witness of the fall, and the noise was perceived only by the occupants of the mill located below the viaduct.

The workmen of the enterprise, who lived about 325 feet above this mill and about 650 feet from the south abutment, heard nothing of it, the wind having carried the noise in an opposite direction.  It was not until morning that they learned of the destruction of their work and the extent of the disaster.

One hundred and sixty-nine feet of the superstructure, weighing 450 tons, had been precipitated from a height of nearly 200 feet and been broken up on the rock at 45 feet from the axis of the pier.  The breakage had occurred upon the abutment, and the part 195 feet in length that remained in position in the cutting was strongly wedged between walls of rock, which had kept this portion in place and prevented its following the other into the ravine.

Upon the pier there remained a few broken pieces and a portion of the apparatus used in swinging the superstructure into place.

Below, in the debris of the superstructure, the up-stream girder lay upon the down-stream one.  The annexed engraving shows the state of things after the disaster.

Several opinions have been expressed in regard to the cause of the fall.  According to one of these, the superstructure was suddenly wrenched from its bearings upon the pier, and was horizontally displaced by an impulse such that, when it touched the masonry, its up-stream girder struck the center of the pier, upon which it divided, while the down-stream one was already in space.  The fall would have afterward continued without the superstructure meeting the face of the pier.