Stone Age of Command
Consider a commander before 1800 [C.E.], sitting in his capital and preparing to launch a war. The sources of strategic intelligence open to him included books—Napoleon, for example, is known to have read every available description and military history of Italy before setting out to conquer it in 1796, and Caesar...probably did the same—as well as maps, however primitive; from these and from the newspapers that began to be published early in the seventeenth century one could glean general information concerning the theater of operations, its resources, it climate, and the nature of the people inhabiting it. This written information was supplemented—or in some periods (such as the almost bookless early Middle Ages) replaced—by oral sources, the tales of traveling merchants, artists, pilgrims. To obtain more specific geo-military information about such things as roads, fords, bridges, and fortresses and about the enemy's moves and intentions, it was necessary to rely on diplomats and spies. The two were often indistinguishable, and still are.
As even a cursory glance will reveal, each of these sources had its own strengths and weaknesses. Some were insufficiently specialized to bring in the specific information that a commander might need, while others were of questionable reliability. Intermittent at the best of times... the flow of information was likely to be reduced still further upon the actual outbreak of hostilities, thought the absence of continuous front lines and the inability of armies to police extensive tracts of territory meant that it was unlikely to dry up altogether.
In the absence of...regular mail service...the speed at which information was able to travel varied greatly. Rumor, especially concerning 'great events' such as a battle won or lost, moved fastest of all—speeds in excess of 250 miles a day are on record—but only at the price of the subject matter being neither selective nor reliable. On the other hand, books, maps, and travelers could hardly be expected to move at more than a walking pace, say ten or fifteen miles a day over extended periods. Somewhere in between these extremes came the reports that agents, stationed in friendly or hostile territory or else reporting on the moves of some neutral ruler, sent back to their employer. When properly utilized and taken together, such sources were often able to present a commander with a fair basis for strategic planning. But their limitations—especially in regard to speed—were such that their usefulness for operational purposes in the field was always questionable.
If obtaining long-range enemy intelligence always constituted a problem, so did communicating with one's own forces. In the present day of radiotelephone and data links it is difficult to recapture the sort of utter isolation that ensued until about 1900 whenever detachments were sent out or an army was separated into several forces. Hannibal in Italy, to cite one extreme example, is said to have had no idea of what the second Carthaginian Army under his brother Hasdrubal was up to until the Romans informed him by tossing Hasdrubal's severed head into his camp. Napoleon at Bautzen in 1813 could do nothing to communicate with Ney, on whose advance the outcome of the battle depended, even though their respective headquarters were less than ten miles apart.... For thousands of years before that, the speed at which field armies could communicate with each other was essentially limited to the speed of the horse—say no more than ten miles per hour on the average, given conditions that were not too unfavorable and over comparatively short distances.
The fact that communications were slow and insecure explains why commanders were always reluctant to send out detachments (the term, remaining in usage until the middle of the nineteenth century, speaks for itself); once detached, they would become all but impossible to control. Nor does the remedy—the establishment of proper strategic units capable of independent action—appear to have suggested itself before the end of the eighteenth century....