It's very easy to find information about the great feats of Roman engineering, but I've managed to scrounge very little information about the actual people. I know of Vitruvius and Pliny the Elder, but I'm more interested in the common engineer, like the military architecti and other immunes, and especially in civilian engineers, unaffiliated with the army.
Did the engineers who oversaw the construction of urban buildings come from the army, or vice-versa?
I'd also love any relevant (and ideally interesting) sources.
We know of large builders societies ('collegia' is a common term but may not be the only applicable term of reference) throughout the Roman dominion - for example, in Ostia ( http://www.ostia-antica.org/regio1/12/12-1.htm ). It seems logical to me that associations like these, which seem to have a level of political influence also, would provision their members with training so as to maintain their position. Ostia is a good place to study since it's only 30km west from Rome, survives very well archaeologically speaking, and was of critical importance to the city of Rome in terms of logistics, even when the two harbours north of it were constructed in the 1st century CE.
For a more in-depth review of the builders in Ostia, check out the following - http://www.sedhc.es/biblioteca/actas/CIHC1_072_DeLaine%20J.pdf