Lack of technological progress in late Roman Empire

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A tremendous site on Roman engineering with lots of good articles covering a wide array of topics to download (PDF or HTML). In English and Spanish: http://traianus.rediris.es/

Btw Falsa alarma concerning the supposed pound lock:

In his official correspondence as governor of Pontus and Bithynia with the Emperor (Epist. 10.41) Pliny suggests to Trajan a canal to obviate vehicular transport between a lake in the territory of Nicomedia, lying to the east of that city, by connecting this Lacus Sunonensisl with the Propontis (fig. 1). The Emperor's reply (42) shows that he would not be deterred by the elevation of the lake even if the army technicians (libratores2 or architecti) to be obtained from Iloesia, or sent by himself from Rome (cf. 41.3), should establish a higher figure than the 40 cubits (60 feet) tentatively claimed by local talent. Trajan's one concern at the moment is the danger of draining the lake away3 by opening such a canal down to salt water. Turning to Pliny's second letter on this subject (10.61), and comparing its 2nd section with the 3rd and 4th, we see that he was weighing alternative projects:

I) He would construct a canal merely to reach the bank of a river flowing into the Sinus Astacenus, that arm of the Propontis at the east end of which lay Nicomedia. He is proposing to leave a narrow dyke between canal and river, so that the heavy freight of 41.2 (marble, farm products, firewood, timber) could be lowered or rolled down to boats on the river. He must have had in mind a slipway (diolkos, 'haul-over'), much used to overcome differences of level. If the canal was at that point parallel to the river, it could be closed by a single floodgate regulating outflow into the river lower down. This plan may have been advanced as an entering wedge, involving a minimum of time and outlay. In both respects it would be likely to commend itself to Trajan, along with other preparations for the war with Parthia then impending. It might well prove the preliminary step towards a navigable canal from the lake down to sealevel in the harbor of Nicomedia.

(II) Better still, to ignore the small river that emptied into the Bay but brought down no water from the lake, and to dig a canal for the whole distance (18 km.). That the Emperor's concern lest the lake be drained away might be relieved, Pliny makes it clear that he plans a narrow canal (fossam . . . artius pressam, 61.4); that he would completely close the natural outlet of the lake at its east end, 6 km. due west of the Sangarius, thus supplying his canal with su5cient water from the lake, thereafter flowing westward. The need of an engineer being obvious, he will write to the governor of Afoesia Inferior, the nearest commander of an army, requesting him to send a librator. In case the volume of water in the canal should prove excessive, he thought the current could easily be checked by cataractae.

SOURCE: Frank Gardner Moore: Three Canal Projects, Roman and Byzantine, in: American Journal of Archaeology, Vol. 54, No. 2. (Apr. - Jun., 1950), pp. 97- 111