Along the old road of Bistoon to Takht-e-Shirin and Sarmaj there are gigantic bases of the famous Khosrow Bridge. The construction of the Khosrow Bridge is attributed to Shah Khosrow Sassanid. The Khosrow Bridge is the only bridge that the Arabs crossed, and after passing through Takht-e-Shirin and Sarmaj went Nahavand and defeated Yazdgerd III, the last of the Sassanide rulers in that city. The Khosrow Bridge with the passage of time, has sustained abundant losses, in such a manner that in Safavid period this bridge was unusable. For this reason, at that time another bridge was built on the Dinvar Ab River, about 1 km. beyond the former bridge.