The Austro-Hungarian Empire, at the end of 1800, planned a series of fortifications in high Cadore to face attacks from the north, towards Val Pusteria and the Isarco Valley, by the new born Italian State. The first fortifications were built between 1884 and 1892 to the north-east of Tre Sassi, in the territories of Sesto, Landro, and Prato Piazza. Later on it was decided to block the entrance to the Valparola Pass by building a further fortification, the "Tre Sassi Fort".

The planning of the fort went on for years and the construction works were begun only in the 1898 summer.

The fort was equipped with two 80mm cannons pointing at south. Two 60mm fortress cannons were pointed at the Falzarego Pass. A rotating armoured cupola on the south-east bastion was meant as observation post and pointing place during combat. Another bastion was placed near the entrance.

The windows were provided with iron bars and could be protected by heavy steel shutters.

Rooms were heated by cast-iron stoves and lit by oil lamps. Water was supplied by the rainwater from the roof and partly by pumping it from the Lake of Valparola. In the basement there was a small crypt with three locules.

The fort and the annexed "provision warehouse" could accommodate over 100 soldiers.

On the 5th July, 1915 the fort was bombarded by the Italian artillery placed at the Cinque Torri; it was hit by 210mm mortars and smaller calibre guns. On the very first day, the fort was seriously damaged, since the walls of the outdated building were not able to resist the fire. It was hit by as many as thirty shells, three of which pierced the roofing, as it can still be seen today.

The troops were no longer able to resist. There were many victims and therefore the fort was evacuated.