I've heard many stories about Romans and their excellent "castra"s (forts/camps). With some of the pictures I've seen on the internet I'm wondering how Roman troops were able to construct such organized forts so quickly. Especially ones with stones and permanent building materials!
I've been able to find plenty of information on the design of the camps, but next to nothing on the actual construction of them, so I thought this would be the place to ask!
Vegetius gives a brief explanation in De Re Militari: http://www.digitalattic.org/home/war/vegetius/index.php#b306
A more speculative work, although based on archaeological evidence, is The Construction of the Roman Legionary Fortress at Inchtuthil, by Elizabeth A. M. Shirley. Shirley uses what we know of the fortress, along with Roman building techniques and combines them with labour estimates from pre-modern sources and, on occasion, experimental archaeology to work out roughly how long it would take to construct the fortress. It's well worth the read: https://www.dropbox.com/s/vjtowrwgvfbihiq/The%20construction%20of%20the%20Roman%20legionary%20fortress%20at%20Inchtuthil.pdf?dl=0
What it essentially comes down to is man power. The Romans had access to a lot of it and, as the old saying goes, many hands make light work.