The great empire formed by the Achaemenid Empire, which had three capitals of Susa, Ecbatana, and Babylon, needed new roads. This resulted in the rising importance of Lorestan. These roads continued to exist until the Sassanid dynasty. During that time, the road connecting Ctesiphon with Isfahan passed through the city of Shapourkhast and Kashkan River. Therefore, a bridge was built over the river. The remaining of other bridges from a long-ago proves the importance of this road and area.
Some of the researchers and archeologists such as Demorgan and Dr. Karimi believe that the main bridge built over Kashkan River was destroyed by the Iranian themselves in an attempt to protect the city from the attack of the Arab army. Later, the Arabs built the current bridge one hundred meters farther than it.
Others believe that the current bridge is reminiscent of the Sassanid dynasty and has been repaired later. However, according to the tablet written in Kufic, which is now kept in Falak ol-Aflak Museum of Khorramabad, the bridge belongs to the fourth century AH and is attributed to Abul Najm Badr inb Hosnavieh. It is estimated to be built between 389 and 399 AH. This means that it took about ten years to finish the bridge. The mentioned tablet was carved into the mountain, close to the bridge. It was damaged during the road construction in the Pahlavi dynasty and was later moved to the museum in Khorramabad.
Despite the damages and lack of repairs, Kashkan Bridge has kept its glory and magnificence. This historical bridge has been mentioned in the book by Hamdollah Mostofi by the name of Kazhki. The word Kashkan consists of two parts of kash and kan or ko, the former meaning near and the latter meaning the edge or coast of the river. Kashkan is an east-west bridge. It has fourteen piers and twelve vaults. The vaults are located far from each other and resemble resting areas. They could have once been used as caravanserai and resting places. With a length of three hundred and twenty-six meters, a height of twenty-six meters and width of eleven meters, Kashkan Bridge connects to sides of the valley.
Materials from local resources have been gathered and used to build the bridge, including the rocks from the bed of the river, limestones from a mine, fifteen kilometers away from the site. The large river rocks have been used in the core of the piers. Combined with mortar and plaster, the strong piers of the bridge have resisted humidity and erosion during so many years.
Kashkan Bridge was registered as a national heritage of Iran in 1382 SH.