CHAPTER I

3.

The Strategical Aspect of the Opening Campaign

 

The Army of Invasion had two ultimate bases of operatiOn. These may be taken to be Cologne for the force in Lower Germany, and Vindonissa for that in Upper Germany. The objective of both forces was the enemy's army, which must be destroyed. That army was not likely to be met north of the Alps, nor indeed north of the Po, for reasons partly of time, partly of strategy, which were obvious to both sides. The theatre of war was likely to be the great plain of this river, that plain which has been the scene of more fighting in the course of history than even have the Low Countries. The immediate geographical objective, therefore, of the Army of Invasion was the section of the Po between Placentia on the west and Hostilia on the east. At the former place was the crossing of the river by the great highway which led south-east, skirting the Apennines, to Ariminum and so to Rome; and this road would have to be pursued by a force crossing any of the Alpine passes on the west and north-west of Italy. And at Hostilia was the second chief crossing of the river by the road which ran from Verona on the north to join the great highway at Bologna, fifty Bononia miles to the south; and by this road an army marching by any of the northern passes down on Italy would have to come.

It was therefore necessary for the Army of Germany to cross the Alps as speedily as possible. The natural difficulties of the passage of the mountains in early spring by a large force, as well as the problem of supplies, made it expedient for the Vitellians to divide their army. Moreover, it was important to secure Gaul, as this country lay on the flank and in rear of the advance, and further to increase the numbers of the invading army by Gallic reinforcements swept in during the forward movement. But if the whole army marched through Gaul and over one of the western passes, the delay caused by the long detour might well imperil the success of the whole campaign. Therefore it was decided that the Army of Germany should remain divided, and that two columns of invasion should march at once. The Vindonissa column was to proceed direct from UpperGermany to Italy; the Cologne column, as it may be called, was to march through Gaul, and strike thence east­wards over one of the western passes of the Alps. The distance to be marched by the Cologne column was nearly three times as great as that of the other. It would arrive later at the objective, and there join the Vindonissa army, should the latter need help.

The Army of Defence had also two ultimate bases of operation—Rome for the Army of Italy, and Aquileia for the Army of the Danube. Both of these were similarly many miles away from the river Po, and, besides this, the concentration of the whole or, at least, part of the Army of the Danube at Aquileia must first be effected. A diagram may serve to illustrate the strategical position at the beginning of the campaign.

Although the distance from Rome to the objective was longer than that from Vindonissa, the time taken by an army marching from Rome would be much shorter, as the natural difficulties which hindered the pace of the Vindonissa column were far greater, and, as it proved, these troops indulged in some petty fighting with the tribes north of the Alps before they set out resolutely on the road.

 

A. Strategical 0pportunities of the Othonians.

Until the Danube army arrived in North Italy to co-operate with them, Otho's troops in that country were so greatly inferior in numbers to the approaching invaders that their only possible strategy at first was a defensive one. It is true that such a strategy, unless it were unexpectedly crowned by a decisive victory on the field of battle, could never be expected to end the war.

Defence was forced upon the Army of Italy until their comrades should arrive, but only for so long. For defence pure and simple sometimes wins battles, but wars scarcely ever.

It was therefore, above all, important to retard the advance of the Vitellians into Italy by every possible means. All Othonian efforts in Italy had to be directed at first to secure this end, and to give time for the Army of the Danube to arrive. The questions, therefore, which arose were two. Firstly, what precise line of defence should be chosen? Secondly, what means of delaying the enemy's march could be employed?

( I) Two possible lines of defence suggest themselves at once to a general who wishes to defend North Italy, namely, the Alps and the Po.

But for Otho the blocking of the Alpine passes was impossible. In the first place, had he even wished to block them, time, distance, and numbers forbade this. Actually he had in North Italy in January AD 69 but one small regiment of horse, the ala Siliana, and this quickly turned traitor to his cause. The troops in Rome could scarcely reach the Alpine passes on the north and north­west before the troops of Upper Germany had seized them. And it would be madness for them to block the western passes, whither they might have arrived in time, when the foe advancing from the north would already be down in the plain of the Po. But even if the Vitellians delayed their approach, and thus gave Otho time to block the passes (and he could not count upon this for a moment), the Emperor was quite uncertain which route or routes his foe would choose. The Army of Italy, scarcely twenty-five thousand strong, would have been distributed along the chain of mountains in isolated, widely separated fragments. A reverse suffered in any single pass would snap at once the chain of resistance. The whole scheme of defence would have been destroyed, and the entire army would have been in danger of piecemeal annihilation.

In the next place, the proper method of defending a mountain ridge is not the blocking of the passes, when several such passes over the ridge exist. To place a division sitting on top of each pass in entrenchments, however strong, is but to court disaster. No mountain barrier, whether Himalaya or Pyrenees, Jura or Alps, ought to be defended in this way, or ever has been for long successfully defended in this way. Picquets and outposts, varying in strength, must be placed in the actual passes. But the main Army of Defence must be kept on the more level ground behind the ridge, concentrated and as near to the issues of the passes as the nature of the ground allows. From such a position it can deal a vigorous blow at its foes when these, forcing back the outposts, struggle by one or more passes with difficulty over the mountains, and emerge more or less exhausted upon the lower ground beyond. It is then that they must be attacked, before they have recovered from the stress of the passage of the heights, when a dangerous country lies immediately in their rear, and when, if they have chosen to cross by more passes than one, the detachments of their troops are perhaps separated by the difficult foothills of the mountain ridge. Then the Army of Defence, perfectly informed by its outposts of the advance of the enemy, with its communications from the flanks to the centre running easily over the more level country which the army occupies, can move to the attack with vigour unimpaired and confidence high, and by a tactical offensive give its strategical defensive the victory. Such was the strategy by which, for instance, the Argives ought to have defended their northern rampart of mountains against King Agis of Sparta in 418 BC. Such is the strategy by which Italy today would defend her Alpine barrier against a foe to north or west of it.

Unhappily, Otho had neither men enough nor time enough to choose this, which otherwise would have been the right, method of defending Italy. He was compelled to abandon all thought of holding the line of the Alps. He could not prevent the enemy's columns, marching by widely different routes, from concentrating in the plain of the Po unhindered. In modern history, in the Napoleonic wars and in the fighting for the liberation of Italy, "the battles lost or won at the foot of the Alpine passes, and in the vineyards of the great northern plain, Rivoli, Marengo, Magenta, Solferino," decided then too the fate of Tuscany, Rome, and the South. As Otho could not guard the foot of the passes, he must fall back upon the second natural line of defence—upon the river which flows through the great northern plain and its vineyards.

This line could be more easily defended. To the west lay the great fortress of Placentia, south' of the river, placed upon the military road where it crossed the Po, and guarding the passage of the river. Placentia if garrisoned strongly and resolutely held would be an invaluable "pivot of manoeuvre" for Otho's defending army, which, with its left flank secured by the fortress, could deploy eastwards along the river in safety. In the same way the crossing of the river to the east must be secured and defended, and at the same time the communications with the Danube army at Aquileia must be kept open and safe from the enemy. A strong garrison at Verona or at Mantua would best achieve this double object. It was vital to Otho to take precautions against the risk that the enemy would come down upon Italy by the Brenner Pass and seek to thrust in between his own army and that at Aquileia, severing the communications between these. At least the Mantua-Hostilia line must at all costs be stoutly defended.

The Army of Italy, therefore, should be spread along the line of the river from Placentia to Hostilia, with special concentration of strength at both ends of the line. And as at the western end the fortress in itself offered a means of strong defiance, the bulk of the defending forces must be directed to the eastern part of the line of defence.

This line the Vitellians would doubtless assault with vigour. But it was unlikely that they would try to break it in the middle, at least at first, or that, if they tried, they would succeed in the attempt. The river here is wide and deep, with shifting sandbanks and dangerous eddies, and its current, swollen in spring, is impetuous. It was far more probable that they would attack one of the two ends. A successful forcing of the eastern end would indeed be ominous of disaster for Otho. His army here must see to it that this did not happen. But the point of attack nearest to the most probable place of concentration for the Vitellians in North Italy was certainly Placentia. If then the enemy combined to assault this fortress, if they even forced the passage of the river here, then at once the advantage which Otho possessed in his double base of operations would come into play. For as the Vitellians advanced down the great road from Placentia, the Othonians defending the river could retire before them unhurt, and fall back upon their second base Aquileia. This would compel the enemy to choose one of two courses of action. They might either neglect this force or pursue after it. If they dared to neglect it, and to press on regardless down the great highway for Rome, by so doing they would expose their own line of communications defenceless to the force at Aquileia. This then, strengthened by the arrival of the Danube army, would sally forth to cut the line. Now it is one of Napoleon's sayings that the secret of war lies in the communications. It is true that under exceptional circumstances an army can afford to cut itself loose from its line of communications with the base—when, that is, it is prepared to live entirely upon the country through which it is marching. But for the most part in all, warfare, ancient as well as modern, an army needs to keep its communications open with some friendly base in the rear of its advance for the safe convoy of supplies and reinforcements, and if it is invading a hostile land it is likely to be extremely sensitive as to the perfect safety of its line or lines of communication with the rear. By neglecting this principle Alexander at Issus was trapped in a hopeless position, unless he won a great tactical victory. Napoleon at Madrid hurriedly abandoned all his year's schemes for the conquest of Portugal because a small British force moved boldly out in the far north of Spain to threaten his line of communications with France. Therefore a Vitellian invading force advancing down the road to Rome was not likely to allow the enemy to cut the one line by which reinforcements could come to it, the one line by which its own retreat, in case of disaster, was secured. Threatened by an advance from Aquileia, the Vitellians would surely turn to face the advancing foe. They would then find themselves in a position which is the most hazardous position for an army compelled to fight a decisive tactical engagement. This is the position technically known as that of an army with its "front to a flank."

As a general, if not his army, must always take into account his position in the event of defeat as well as in that of victory (unless he is staking all on a single throw, and wishes for no choice save that between victory and annihilation), the Vitellian commander could not contemplate with equanimity an advance which might compel him at any moment to form front to a flank in face of the enemy, if he was unwilling to surrender altogether his line of communications to their mercy.

If then the Vitellians forced the passage of the river at Placentia, it was more probable that they would not straightway pursue their march south­east along the road. They would rather follow upon the heels of the retiring Othonians towards Aquileia. This would suit Otho well. He would be retreating in the direction of the advancing Army of the Danube, and the aim of his defence, of the river—concentration with this—would be achieved. Doubtless it was better not to abandon the whole of North Italy to the invader, for political if not for military reasons. The invader should not be allowed to cross the river without fighting, at least to prevent murmurs and discouragement in Rome and among the Emperor's troops. But if, by fighting, the foe forced the passage at Placentia, even so the tactical would not be a strategical defeat for Otho.

(2) The first means of delaying the Vitellian advance was, therefore, the occupation in force of a line of defence on the river Po from Placentia to Hostilia. Twenty thousand or twenty-five thousand men could surely maintain their position here for some time, helped, as they would be, by the river. It is true that this could be but a temporary measure of passive defence. "The defence of rivers has hardly ever been successful for any length of time. Neither the Danube nor the Rhine has stopped armies." A river, like a mountain range, is an insurmountable impediment which is invariably surmounted." The Po could not be permanently held, any more than was the Tugela, in the face of repeated and vigorous attempts to force the passage, especially when, as in both these cases, thanks to inferior numbers or irresolution, no counter-stroke over the river could be dealt the assailants by the defending army. But as a means of delay rather than as a permanent obstacle the river was of the greatest value to the Army of Italy.

The second means of delay was the fleet. The command of the sea was absolutely Otho's. An invasion of North Italy from Germany, it might seem, affords the least possible chances that the command of the sea should have any influence at all upon the conduct of operations. No more unpromising field for the application of the pet modern theory, it might be urged, could possibly be found. Yet none the less, as in the days of the second Punic war, although for different reasons, so in the civil war of AD 69, the invader of Italy had cause to regret the fact that the control of the sea rested with the defender.

The reason for this in AD 69 was that the flank of an army which proposed to cross one of the western passes over the Alps was vulnerable from the sea. If Otho could spare the troops, a force could speedily be conveyed on shipboard to Fréjus, and there landed. With the fleet as its base it could march up country to threaten the right flank of a column crossing the Alps by the Mont Genevre or Mont Cenis Pass. If the enemy turned upon it with superior numbers, it could retreat to the coast as securely, for example, as the British army of the Peninsula in 1808-1809 fell back on the fleet at Corunna when pursued by the thronging battalions of the French. And every soldier thereby detached from the invading army, every hour's delay to the final concentration of the Vitellians in North Italy, was so much pure gain, to the Emperor.

This, indeed, would be but a minor operation; intended to cause a diversion, and by no means the chief drama to be played in the theatre of war. But, as its object would be entirely consistent with, and favourable to, the development of Otho's main strategical plan for the beginning of the campaign, it would be entirely justifiable. The expeditionary force to be sent with the fleet must not, indeed, be so large that the main army on the Po would be too weak, owing to its absence, to fulfil the task of defence assigned to it. Nor, again, must it be so small that its intended menace could be contemptuously neglected by the enemy. Some expeditionary force must be sent, if the fleet were to be of any service at all. Thus when Napoleon's line of communications with France in his invasion of Italy in 1796 ran along the coast through Savona, the British fleet, although it "completely dominated the Mediterranean littoral," was quite unable to threaten these communications, since it had no force on board with which to strike a blow at them. The use of an army for such operations, conveyed by and based upon a fleet, however inferior in numbers this army may be to the enemy, is a vital element in the strategy of the command of the sea, although this principle seems hard to realise from the days of Pericles down to our own generation.

If then Otho could spare a few thousand men from the Army of Italy to be carried on ship and disembarked at Fréjus or some other port on the coast of Provence—the "Province"—this might be a second useful means of delaying the advance and concentration of the enemy till such time as the Army of the Danube arrived at Mantua.

Then at last would come the time for offence, and Otho's united army could be sent against the enemy to hurl them back through a land long since exhausted by their stay in it; back against the grim barrier of the mountains which cut them off from safety—back with weakened strength and diminished numbers, to perish, starved and fighting, penned up against the Alpine wall. "Happy the soldier to whom fate assigns the part of assailant." Or perhaps Otho need not wait for the arrival of the entire Danube army when once these were hard at hand. "The essential in war is not the massing of troops but their co-operation." "Envelopment, not mere weight of numbers, is the true secret of decisive success." Some more daring plan of attack might suggest itself which promised speedier victory than the frontal attack by a united army. Could not the stubborn fighting, the many weary miles of marching which lay between the river and the mountains, the last desperate stand of despairing men,—could not all this be avoided by some masterpiece of manoeuvre and surprise?

But all such plans must for the present be delayed until the Danube army should arrive! Meanwhile one step was enough. Strategy cannot look to the horizon lest she stumble in the ditch at her feet. "No plan of operations can with any safety include more than the first collision with the enemy'smain force." So for the time the Army of Italy should make resolute defence along the line of the Po, and the command of the sea should be used to assist it to delay the Vitellians' advance.

This strategy surely promised well. It had, however, two defects in chief. It failed to prevent ultimately the enemy's concentration in the plain of the Po, though delay might be caused by the fleet. And the strategy of defence, however temporary, might at any time impair the confidence and morale of the men of the army on the river, and especially so at a time of civil war, when all the troops were excited and impatient. For the game of war as played in the field is anything but the War-game of the drill hall. 'Would the Guards, the flower' of the Roman army, consent to stand for some weeks on the defensive against a hated foe? If they obeyed such orders, would their military fire and zeal not be impaired? Such questions had to be considered by the Emperor. Yet he knew that his men were devoted to his cause. The strategy of defence on the river was the wisest for him, and Otho might well feel that he could rely upon his men for any manoeuvre—even that most dispiriting one of waiting to be attacked. Further than the Po he would not retreat. Not though the Apennines in spring are deep with snow, and their mountain tracks hazardous and well-nigh impassable, would he fall back under cover of their shelter, and seek to lure the foe on to venture into their recesses or perhaps be ensnared between them and the sea. Retreat to the river was far enough. Beyond the river the one maxim laid down by our English general for an invaded country held good for Otho and his men: "No foot of ground ceded that was not marked with the blood of the enemy."

 

B. Strategical Opportunities of the Vitellians.

The Vitellians, on the other hand, enjoyed the advantage of being the attacking party, but very few advantages besides. The courage and confidence characteristic of good troops who move to the attack, and apt to be lacking in those kept on the defence, might certainly be theirs. Yet perhaps this would hardly do more for them than compensate for their original inferiority as troops of the line to the Guards. Clausewitz's familiar assertion that the defensive form of warfare is in its nature stronger than the offensive, causes very great searchings of heart to the strategists among his countrymen today. But if ever a strategical position were wanted to justify the assertion, that of the spring of AD 69 might seem to be the one desired. For then the Vitellian chances of prosperous attack seemed somewhat meagre compared with the Othonian of happy defence. The most obvious, perhaps the only possible, strategy for the invaders was a rapid descent over the mountains to the plain of the Po, and a frontal assault upon the position garrisoned by the Army of Italy. Time was of the most vital importance to the Vitellians. They must hasten to move upon Italy in time to anticipate a possible blocking of the Alpine passes. They must hasten to fall upon the Army of Italy before the Army of the Danube had time to come to its aid. Only if they could crush the former force before the arrival of the latter in strength would they have the undoubted superiority henceforward in the strategy of the war, should the war continue. The movement upon Italy in two columns by different passes was necessary. The column which, travelling by the nearer route, first arrived in Italy must, if strong enough, attack the enemy at once; if too weak, or beaten in its onset, it must wait for the coming of the second column to reinforce it. And the race between the reinforcements of both sides would in truth be an anxious one. Speed, concentration, and frontal attack seemed the sole means to the Vitellians of achieving success. And the strength of the defenders' position combined with the means open to them of delaying the assailants' approach might neutralise the advantage of numerical superiority enjoyed by the latter.

An alternative strategy to this of concentration and frontal attack might be considered. The "strategy of penetration" justly wields much fascination, and for modern war has all the support of Napoleon's favourite practice behind it. If the Vitellians could thrust boldly between the two fractions of Otho's gathering army, could they not defeat them in detail? The Brenner Pass in the north offered the easiest access to Italy of all the Alpine passes, and led straight down to the very centre of the hostile position. Could the Vitellian generals use the advantage of superior numbers which they enjoyed at the outset, and drive in a great wedge of their own men, penetrating the defenders' lines midway between Placentia and Aquileia? This alternative strategy deserved consideration by the Vitellians at the beginning of the campaign. But the reasons which caused Caecina to reject it were adequate.

Such were the strategical opportunities of both sides at the outset of the struggle. No campaign ever yet followed precisely the course marked out for it by the strategist. The weavers at the loom of war might think to have but a common and familiar pattern for their work. But the designer who cuts out the cards for them may have indulged a free fancy in the pattern which he gives them.