Shushtar

The city of Shushtar in southwest Iran was located on the Persian Kings Road, which connected Susa with Persepolis. 
Alexander the Great crossed the Karun River here in 331 BC.

Already in the Achaemenid period, the construction of an artificial canal system had begun, which was used for irrigation of the sugar cane fields as well as for driving numerous mills. 
After the defeat of Emperor Valerian in 260 AD, many of his Roman soldiers, who had been captured by the Sassanidians, were sent to build and expand the irrigation system. The resulting 500-meter-long "Caesar's Dam" (Band-e Kaisar) is considered the most easterly Roman bridge and Roman dam. 
In 2009 the dam together with the historic irrigation system in Shushtar was declared a World Heritage Site by UNESCO. 

In July, the average temperature in Shushtar is around 46 degrees Celsius, but temperatures have also been recorded above 50 degrees Celsius. But when I visited it in November 2019, it was a pleasant 29 degrees.