Lack of technological progress in late Roman Empire

[conon394]

I found the evidence, provided kindly by Flavius Promotus here, rather scarce, more so, because we have so many depictions of square sails (surf the navis database) that I find the distinct lack of lateen sail depictions suspicious. I dont feel the rather indirect literary evidence can counter this lack sufficiently enough to speak confidently of a general use of lateen sails in late Roman times.

Eleatic Guest, why suspicious? The Lateen sail is not better than a square sail just better at some things, worse at others and with its own set of drawbacks. I would agree the lateen is certainly a later development of the late classical world, but the broader concept of a fore-aft rig is well documented from at least the 2nd century BC with the sprit sail.
Thus light coasters and river craft already had an alternative to the square sail.

Casson has one other nice bit of evidence/logic – brails. The fact that the Classical square sail could via it brails be turned into a quasi –lateen, is to my mind fairly significant. On the one hand it reduces the need to add a lateen to a square rigged ship and provides a nice basis for where the lateen might develop from.