Lack of technological progress in late Roman Empire

[Eleatic Guest]

I am looking for evidence concerning possible Roman arch dams. An arch dam is of a convex shape, thereby transferring the water thrust to the valley sides (the other basic type are gravity dams, which resist the water pressure through their sheer mass. Practically all ancient dams were gravity dams).

Could someone check out the relevant passage at Procopius? Does he explicitly comment on the structural advantages of an arch dam?

Most interesting is, however, the dam built near Dara, Turkey. Procopius of Caesarea (AD 490-562) stated that Chryses of Alexandria, did not build this barrier in a straight line, but in the form of a crescent, in order that its arch, which was turned against the stream of the water, might be able to better resist its violence. The upper and lower parts of this barrier are pierced with apertures, so that, when the river suddenly rises in flood, it is forced to stop there and to flow no further with the entire weight of its stream, but passing in small quantities through the aperatures, it gradually diminishes in violence and power....

This statement shows that the Roman engineers understood the principle of arch dams and flood retention basins. However, recent preliminary surveys found no trace of the arch dam--only the remains of two gravity wing walls. Nevertheless, in the 70 m wide gap between the wing walls there might have been a slightly curved dam about 5 m high.