What is particularly fascinating is that there must have been an industrial and technical infrastructure to support the design and manufacture of these kinds of devices - we do have mentions in the literature of other, similar devices - but there seems to be no obvious trace of that infrastructure - or the objects that it produced. What kinds of things did they make? And why did they not have a greater impact on history? Of course, this is a variation on the Needham Question (http://www.bbc.co.uk/radio4/history/inourtime/inourtime_20061019.shtml).