Simplify – but not, please, in the manner of, say, Liam Fox – your image of Europe. Envisage its elementary geometry as an arrowhead pointing into the ocean from Asia. The Mediterranean and Atlantic mark the edges. Roughly bisecting the angle is a long watershed of highlands and boglands, from which almost all major rivers flow, splitting the continent into two natural economic zones. Strenuously, over millennia of cabotage, trading, colonising and empire-building, each zone took shape as a practical arena of long-range commerce, uniting, in the case of the Mediterranean, coasts and hinterlands from the Strait of Gibraltar to the Levant and the Black Sea, and, along the Atlantic fringe, from the mouth of the Guadalquivir to the innermost recesses of the Baltic. The history of Europe can be written in terms of the efforts to create and ultimately to integrate the two zones.

Heroic books by Cyprian Broodbank on the Mediterranean (The Making of the Middle Sea, 2013) and Barry Cunliffe on the Atlantic (Facing the Ocean, 2001) have described the forging of each zone. Cunliffe has now undertaken the daunting but vital job of showing how the two economies interlocked. For the pioneers who accomplished the labour of integration it was hard to beat the breakwater. Although Greek merchants used the Garonne and the Rhône in antiquity to bypass Phoenician control of Spain, the overland routes were few and dangerous until Roman times. The two zones were mutually accessible by sea only with great difficulty. Between the Pillars of Hercules a fierce westerly current stoppers the Mediterranean, like a cork in a bottleneck, keeping navigators in their own seas and deterring Atlantic interlopers from invading the Mediterranean by imperilling their chances of returning home. Pindar told his readers not to bother to attempt the passage. Even when pilots in antiquity had worked out the means of penetrating the strait by making use of the undertow along the northern shore, they found sailing conditions in the Mediterranean and the Atlantic so different – the Mediterranean was tideless and tight, the Atlantic turbulent and apparently immeasurable – that few seamen had the experience, confidence or technology necessary to handle both well. Almost all the venturers we know of before Roman times were Phoenicians or Greeks. The latter never got much beyond Andalusia – where, as Matthew Arnold had it, shy traffickers undid their corded bales; for the Phoenicians, as Cunliffe points out, there is no evidence that they made it beyond Galicia, where they went in search of precious tin.

It took four thousand years for what the author calls ‘the two faces of peninsular Western Europe’ to come together. The evidence for how it happened forms mazes and deserts – sometimes bafflingly dense and convoluted, sometimes maddeningly barren and desolate. Cunliffe finds his way through these with skill. Like a searchlight operator, he switches focus continually, highlighting each sea alternately in vivid flashes or, at times, in sustained glare. He starts in the remotest period of antiquity about which speculation is worthwhile and is surely right to say that ‘seafaring was a fact of life’ in the Palaeolithic era. He shows how, from the sixth to the second millennium BC, there was more cultural traffic from the Atlantic to the Mediterranean than the other way round, plotting distributions of megaliths and bell beakers to demonstrate this. He welcomes us aboard with the merchants of Samos and Byblos who sailed to Tartessos – the El Dorado of antiquity – in the first millennium BC. He evokes the doggedness with which Roman generals overcame their men’s distaste for the sea to conquer Carthage and dominate the Atlantic littoral. He turns the comings and goings of medieval shipping into a coherent story. Finally, when his narrative reaches the end of what we conventionally call the Middle Ages, when Latin Christendom was functioning, albeit imperfectly, on both sides of the European watershed, Cunliffe points us towards Europe’s transatlantic expansion and the creation of an Atlantic world.

Along the way, he chronicles the transformation of Europeans’ perceptions of the Atlantic. Among early explorers it was a ‘journey’ or ‘a place for forgetting’. To peregrinatory Irish anchorites of the early Middle Ages, ‘the Western Sea was their desert’. By the end of the story, after Columbus had demonstrated the viability of commercially exploitable routes to and fro across the ocean, the Atlantic had become a ‘destination’. The space available for monsters and mythopoeia shifted westward to the New World.

Cunliffe writes sparse, clear, uncluttered prose that never tires. He is especially good as a historian of shipbuilding: readers can get a better conspectus of the subject from his book than from most dedicated histories. He handles environmental history deftly, acknowledging that climate and geography limit and condition human achievements without determining them. Conventional histories have too much hot air and not enough wind: in the age of sail, winds and currents shaped what happened at sea. Cunliffe’s wind maps make the point. In the Mediterranean, for instance, you can see why the southern littoral can be conquered from the north more easily than the other way round. The maps are staggeringly good, all drawn with great freedom, in defiance of hidebound cartographical conventions. Most are oriented towards the west in order to make the reader adopt an Atlantic focus. The copious illustrations are well chosen, too – always engaging, often dramatic. I could look for hours at the seafarers engraved on the 12th-century font in Winchester Cathedral, where a woman weeps and a man prays while the skipper tensely embraces the tiller, or at the Phoenician ivory in which a lioness gorges on a boy’s throat in an embrace as erotic as it is fatal.

There is little to cavil at. Cunliffe’s resolutely maritime focus does exclude one part of the story of the making of Europe: the laborious exploration of land and river routes across the central watershed. Sometimes the author is tempted into speculative reconstructions of ancient networks. He is also inclined to be generous in treating disputable texts as authentic. I wouldn’t go along with his (to my mind, late) dating of the emergence of a spherical world picture, or his claim that Norse navigators reached Greenland by latitude sailing. It seems more likely that they used the currents and winds that lead westward along the Arctic edge. Nor does he allow for the emporia trading that brought Baltic amber to ancient Greece via Sarmatian traders and the Black Sea. He sees navigation rather narrowly, mainly in terms of the exploitation of winds and currents: coverage of direction-finding and of methods of calculating speed and distance is perfunctory. I wish he paid more attention to the Baltic and the Black Sea – those inner lagoons, respectively, of the Atlantic and the Mediterranean, the existence of which explains why Finland and the Baltic States are European, and why Russia and Turkey might be. I cannot endorse Cunliffe’s inclination to believe in a ‘wanderlust gene’, but I applaud his willingness to broach the subject of the psychology of pioneering. My own ancestors were so unenterprising as to stare out at the Atlantic for millennia without doing anything about it, as if they shared Hesiod’s or Horace’s notorious abhorrence of the sea. Fortunately, not all Spaniards felt this distaste or echoed the Duke of Plaza-Toro’s declaration, ‘If ever, ever, ever, they get back to Spain they will never, never, never cross the sea again.’ But why so many Spaniards and Englishmen share a maritime vocation and why individuals and communities behold the sea with emotions varying from fanaticism to phobia remain intriguing mysteries.

Overall, the total effect of On the Ocean is to encourage a new way of looking at European history using a maritime perspective. I hope it changes the way people think: it is good enough to do so.