Something I always wondered about, considering the dimension of the Roman Empire, is how the 'Roman Post Office' worked, especially for the legion.
During Hadrians time, for example, how long did it take to send a message from Roma to Londinium?
Was there an accurate intelligence/messenger system, and if, how was it organised in those days?
Was there a 'real-time' information system, e.g about an on-marching enemy, and thus a major advantage for the Legions to rely upon?