or make them move by different routes far apart from each other, unless they
could be pretty certain that no enemy was likely to attack those forces in detail.
A contributing factor to this may have been the absence of good large-scale
maps, especially of the kind that can cover entire theatres of war in some detail. To
convince oneself of this fact, one only has to see a Roman itinerary or the rough
sketch that late-sixteenth-century Spanish commanders used in order to march
their forces from their assembly place in northern Italy around the frontiers of
France towards the theatre of war in the Netherlands. 12 Some historians have
gone further still, arguing that the absence of maps itself indicates the inability of
pre-modern people to visualize the world in terms of the two-dimensional space
so vital to operational art. 13 However, this is uncertain.
As late as the second half of the eighteenth century, Frederick the Great, one of
history’s great commanders, is still found using similar methods and labouring
under similar constraints. While maps were improving—triangulation, intro-
duced after the invention of the telescope around the middle of the eighteenth
century, was now used to make them—on occasions, he still considered it
necessary to rely on sketches made by his own hand. Concerning enemy infor-
mation, as the king himself wrote, 14 the most important sources remained
travellers, local inhabitants (meaning, any halfway intelligent peasant), deserters,
and prisoners. To these would be added the spies sent out to explore the enemy
camp, and—something he does not say, probably because he took it for
granted—the cavalry patrols that went to observe it and that might take the
prisoners. On any given day, even the fastest of those could only cover twice or
thrice the distance the army itself could. However, since messages had to be
physically transmitted from mouth to mouth or from hand to hand, ‘active’
methods of obtaining information had their effective range cut in half, owing to
the need to make a return journey.
For the same reason, that is, the slow pace at which information travelled, the
distance from headquarters at which it was possible to exercise effective com-
mand was also limited. Again, relying on the words of Frederick himself, we find
that normally it was no more than about two miles, which meant that fronts were
limited to about four miles. 15 In fact, the one campaign when he tried to carry out
a concentric advance on two separate fronts, during his invasion of Bohemia in
1757, ended in failure. Contemporary critics were not slow to blame him for even
making the attempt. 16 At a time when battles were still being fought by long lines
of men standing shoulder to shoulder, such short fronts limited the number of
troops an army might comprise. This, in turn, explains why, in the view of
Turenne, exercising command over more than 50,000 men was beyond the
capability of a single person. 17 As if to confirm this analysis, bodies of troops
operating beyond the commander-in-chief’s immediate control were known as
‘detachments’. Various considerations, including, above all, the need to expand
the area in which supplies might be gathered and to provide flank security, might
compel a commander to form them and use them. However, doing so always
carried the risk that, when battle was imminent, they would not be available to
participate in it.
14 The Evolution of Operational Art