I recently read about an ongoing discussion in the research of ancient history about the planning (or lack thereof) that went into the foreign policy of roman emperors (especially Augustus, as I understand being the first who actually had the time and power to make such strategic decisions for long periods of time all by himself and not only as part of a ruling elite). I was thus wondering, how that would or would not have been possible, based on the information available to the emperor (what does the land look like, where's the next river, who lives there, where should the borders be drawn). What sources are available today that give information about this?