Never heard of this story about Valerian before ... from Press TV:

Iran plans to restore an ancient bridge which is believed to have been constructed by the captive Roman emperor Valerian in AD 260 in return for his release from the Sassanid custody.

The bridge, named the Shadravan Bridge, is located in the southwestern province of Khuzestan, and is the longest and biggest ancient bridge in Iran.

Director of Shushtar Cultural Heritage and Tourism Organization, Mohammad-Hossein Arastuzadeh, has said that the site still needed to be studied in terms of architectural considerations before any further actions.

The ancient bridge dates back to the Sassanid period (226 - 651 AD). History has it that Shapur I, the second Sassanid king, agreed to free Valerian and his soldiers - who had lost a war against the Persians - on the condition that they build what is today called the Shadravan bridge.

The bridge originally had a total of 44 arches of which only 37 remain now.

The Wikipedia article seems to hint at this 'alternate view' of the fate of Valerian (whom Lactantius tells us met a painful fate), but I can't say anything about the sources ... the de Imperibus Romanis article gives the view most of us (I suspect) learned ...