Hannibal’s legacy: always find the flank

Remarkably, much of the theory and practice of warfare for the last two millennia has been shaped by the events of an August day in Apulia (south-eastern Italy) in 216 BC, when the Carthaginian and Roman armies met on the battlefield of Cannae. The Carthaginians, commanded by Hannibal, had twice defeated Roman armies since invading the Italian peninsula, but now seemed to be cornered by a numerically superior Roman force. Republican propriety required that command of the Romans alternated daily between two consuls and most historians credit Hannibal with offering battle on a day he knew that the hasty and intemperate Gaius Terentius Varro would be calling the shots.

Hannibal deployed his infantry in a linear formation, following the tactical conventions of the time. But he then pulled his centre forward to create a semi-circle facing the Romans, supported by two linear flanks, manned by his steady and reliable African heavy infantry (if in doubt, picture the front edge of a football penalty area). The semi-circle was made up of Gaulish warriors, who fought semi-naked and specialised in wild, screaming charges while wielding broadsword and axe. These shock troops of the Carthaginian army were not the obvious material to face the inexorable discipline of the Roman legions, whose tactical forte was the close, attritional battle. Yet that mismatch was at the heart of Hannibal’s tactical design.

After an initial cavalry engagement, in which the Carthaginians eventually prevailed, the two infantry masses closed to contact and the Gaulish semi-circle was first smashed flat and then turned into a deep V-shaped incursion into the centre of the Carthaginian line. But as the Gauls fell back and Varro sensed victory, the African infantry held firm. Probably due as much to battlefield physics as to sentient command, they wrapped around the Roman infantry, just as the now victorious Carthaginian cavalry returned to the main battlefield. This manoeuvre completed the total encirclement of the Roman army.

The present-day student of Cannae can only pity the legionary at the centre of the Roman advance. Choked by dust, exhausted by the visceral physical labour of close-quarter combat, unable to see more than a few yards, he would nevertheless have been elated by the sense that he had defeated the enemy opposite and that his cohort was advancing. Of course, he could not know that Hannibal’s profound instinct for the character of his own troops, his exact analysis of Roman tactics and his sense of the frailties of his opposing commander had conspired to produce a design for battle of near conceptual perfection. That would only become clear as the Carthaginian wings closed around him and Numidian horsemen attacked from the rear. The legionary fought and died where he stood.

Casualty figures at Cannae are probably apocryphal, but the Greek historian Polybius put Roman losses at 70,000 dead, in what became arguably the most catastrophic defeat in Roman history. In a single day, Hannibal’s historical reputation was made and the theory of double envelopment was born.

The idea of double envelopment — the simultaneous engagement and defeat of both flanks of an enemy position — has had a grail-like significance for military commanders as disparate as Napoleon Bonaparte and Norman Schwarzkopf. Both cited an intellectual debt to Hannibal, but neither could entirely emulate him. Napoleon’s masterpiece at Austerlitz ended with the single envelopment of the Austro-Russian right, while Schwarzkopf pulled off the same abbreviated manoeuvre against the Iraqis in the first Gulf War. Perhaps the nearest any commander in the modern age has come to a second Cannae was Helmuth von Moltke the Elder, in the comprehensive German defeat of the French at Sedan in 1870, and this should come as no surprise.

First Prussia, and later Germany, always faced the strategic inconvenience of a geography that placed them at the centre of Europe and the prospect of fighting on two fronts simultaneously. From Frederick the Great onwards, they became apostles of rapid manoeuvre and large-scale battles of annihilation which would neutralise a single threat while giving them the time and space to address a subsequent one. This could never be achieved by engaging an enemy’s main strength in a frontal assault and, while double envelopment remained the goal, single envelopment – the immutable principle of finding the flank – became the core doctrine of the Prusso-German school of military theory. It still dominates the manoeuvrist teaching of Western military academies today.

No surprise, either, that one of Moltke’s successors, Alfred von Schlieffen, became the most assiduous modern student of Hannibal and author of a seminal treatise on the Carthaginian’s military legacy. Schlieffen’s eponymous plan for the invasion of France at the beginning of the First World War took elements of the tactical design of Cannae and elevated them to the level of military strategy. The line between 216 BC and 1914 AD was clear and unbroken.

So what? Is all this of any interest to Vladimir Putin, Ayatollah Ali Khamenei, the Hamas leader Yehia Sinwar or Xi Jinping? Probably not. But even if they don’t know it, they are following in the footsteps of Hannibal every day. The initial Russian invasion of Ukraine was conspicuously unable to find the flank and the war is currently caught in a grinding attritional slog. Yet in a leap of manoeuvrist imagination, it seems that Russia is exploring the exposed flank of western political resolve by stirring up the nascent conflict between Serbia and Kosovo.

The Serbs always seem caught between two identities: an aspirationally liberal, outward looking Eurocentric sense of self, and a more atavistic, pan-Slavic identity that seeks assurance in Orthodox religion and looks to Moscow for strategic guidance. It is through the apparatus of the older, darker Serbia that Russia is now seeking to manipulate events in the western Balkans, supplemented in all likelihood by the ubiquitous little green men that have become Russia’s weapons of choice in the grey zone of hybrid warfare. If Putin can export the conflict in Europe across the 1500 km between Kyiv and Belgrade, he will have raised the stakes, caught the attention of NATO — and demonstrably found the flank.

So too, it seems, have Iran and Hamas. Shia Iran will have been desperate to stop Sunni Saudi Arabia following Bahrain and the United Arab Emirates in offering diplomatic recognition to Israel; bad enough to be facing off with the Jewish state, but to have a Sunni Arab bloc in the same camp would add a confessional enemy to an existing secular one in a dangerous mix. Time to find the flank.

Novel and imaginative tactics by a supplicant Hamas, combined with an unforgivable Israeli intelligence failure, will soon leave Saudi Arabia with little choice but to join a pan-Islamic chorus of outrage, as Israel cranks up its inevitable retaliation and creates a palpable diplomatic distance from the Saudis. The main victim in this passage of events will be the luckless Palestinian people. But as an example of strategic envelopment – with only the lightest trace of fingerprints on events – Iran has shown a cynical mastery of the genre.

Not all flanks need to be physically engaged. In Joseph Chamberlain’s words, Britain in 1902 was “the weary Titan staggering under the too vast orb of its fate”. Joe Biden probably knows the feeling. The millstone of a trillion-dollar public debt to be serviced in a hostile bond market would circumscribe the strategic ambitions of even the most energetic of US presidents, let alone old Joe. Xi Jinping has his own problems, but he can, with little effort, demonstrate against Taiwan – short of war but with the clearly implied threat of one — in a way that might stretch even the strategic inventory of the United States. America could become committed simultaneously in the eastern Mediterranean and the western Pacific. If Ukraine then becomes the victim of a three-way fight for resources, so much the better for Xi. Without a single shot necessarily being fired, an elegant and global strategic effect might be achieved by simply an implied threat to an exposed flank.

So, Hannibal’s legacy lives on and it’s not difficult to find any number of contemporary examples of single envelopment. There is even a case to be made that the historic party trick of double envelopment is occurring right in front of our eyes. The examples cited above have focussed on the variable geometry of inter-state relationships, but there is clear evidence that a separate envelopment is taking place within societies as well as between states. When fireworks are set off on London’s Edgware Road to celebrate an act of mass murder in Israel, then it is clear that another flank is being opened and engaged, this time within the social fabric of the United Kingdom. And we’re not alone. With the highly politicised banlieues surrounding its major cities, plus both the largest Jewish and Muslim populations in Europe, France is probably even more polarised, while other European countries will face their own dilemmas.

Without seeking to offer any comfort to the Iranian theocracy, Tehran seems to have pulled the strings that have simultaneously engaged a physical flank in the close enemy, Israel, and a cultural flank in the deep enemy, western social cohesion. Moscow is trying the same stunt between the battlefields of Ukraine and the chancelleries of western Europe, while Beijing simply has to bide its time and choose its moment. It’s a long distance from screaming Gauls and gouging legionaries, but the principle of double envelopment, adapted for our times, is there in plain sight.

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