Literary lure of the sea: Philip Marsden explores the global connections of his home in Cornwall

Many writers love out-of-the-way retreats, but few make themselves quite as – apparently – scarce as Philip Marsden does now. Turn off one of the steep-hedged lanes that thread through the Roseland peninsula in west Cornwall, and almost a mile of rough track takes you down to an early-Victorian farmhouse that itself stands on the site of a medieval manor. Swifts wheel above; a lone pheasant gazes curiously at two humans sitting at an outside table; silence reigns. Seen from the land, this isolation seems complete. But the terrestrial is not the only view. For these grounds slope down through tangled growth to an inlet – one of many tiny capillaries into which the huge body of the Fal estuary narrows – and an old landing-stage. When the winds and tides concur, Marsden can take his boat moored there, sail downriver into the Carrick Roads and - as he writes in his new book – "point the bows south towards the flat horizon, and the open sea".

As award-winning travel writer, narrative historian and novelist – of a 1930s Cornish fishing village, in The Main Cages – Marsden has always had a knack of linking the local and the global, the near and the far. In The Crossing Place, he tracked the Armenians and their tragic diaspora. The Spirit Wrestlers and The Bronski House carved strange stories out of idiosyncratic lives on the ragged fringe of the Russian and Soviet empires. The proudly self-sufficient culture and faith of Ethiopia, where he served his apprenticeship as traveller and writer, gave rise to The Chains of Heaven and The Barefoot Emperor. Under his eye, the margins and the metropoles swap places. Outcasts occupy the centre-stage. And the forgotten or patronised backwater turns out to flow straight into the mainstream of history.

Now his own watery backyard gives Marsden another choice anchorage. The Levelling Sea, his "story of a Cornish haven in the age of sail" (HarperPress, £18.99), not only follows the history of the town and port of Falmouth from the 16th to the 19th centuries, and depicts the salty characters who helped transform a piratical hideaway into the bustling, raucous north-eastern corner hub of a trans-oceanic "Atlantic village". In lyric interludes it traces the author's own romance with the sea, a love "as powerful as any human attachment". Yet no love – as the book shows – could ever go more utterly unrequited. Marsden quotes (who else?) Joseph Conrad, who wrote that "the sea has never adopted the cause of its masters".

The book itself, its scenes of well-crafted history and biography intercut with subjective seaborne reminiscences, has something of the episodic, changeable quality of a voyage under sail. "More than in previous books," says Marsden, "I was feeling my way... That's quite dangerous, but it also makes you reckless – like the early saints taking to sea without knowing where they were going or even whether they were going to reach the shore at all. That's the sense I had."

Marsden's own efforts to win the sea's consent, if not to control it, began in infancy. Every year he would come to Cornwall on family holidays and sail around the Fal estuary in his grandfather's boat, the Ratona. "It was only a couple of weeks each year," he says, before late-June showers drive us into the kitchen of the farmhouse where he and his family have moved from St Mawes (his wife is the writer, and Russia specialist, Charlotte Hobson). "But the most intense memories of my childhood were here – possibly because it was slightly rarefied and brief". During the later squalls of young adulthood, he thought of the Cornish coast as "a place where it seemed that the best things happened". The Levelling Sea abounds with stories of mariners who, lost on land, found their feet at sea. During its author's early twenties, he felt "hopeless at everything. But I knew how to handle a boat."

Tanned and lean, he still does. The Liberty – the vintage harbour launch described (and photographed) with a lovingly elegiac eye in The Levelling Sea – has now given way to the "old coble with cutch-brown sails" evoked at the book's close. Meanwhile, their skipper races in competition around the estuary at weekends, on one of the oyster boast crewed by local people who – these days – may well be the builders and plumbers who renovate second homes. As a fledgling travel writer, Marsden would alternate his voyages in the Horn of Africa or the Middle East with productive seclusion – especially through tourist-free winters – in his family's own summer house. "For about ten years, I revolved around it. It was the still point in a rather chaotic life... and a great background against which to write."

The idea of the safe haven as a "springboard" for global adventure propels The Levelling Sea. "I didn't want to write a history of Falmouth because that would be fairly limited," Marsden says. "I wanted this small place to represent a huge story." It certainly boasts the backdrop. Falmouth commands the third largest deep-water harbour in the world (after Sydney and Rio). If geography is destiny, then this exemplary shelter looked set to shine. Yet in medieval times, it nestled at the unruly edge of an offshore island.

Then, lent a fair wind by the buccaneering "rebel state" of Protestant England, came the 16th-century breakthroughs in ship design and seamanship. Those advances saw the marginal mariners of the West Country criss-cross the world as the "British Impire" (John Dee's coinage, in 1577) took on its original, maritime shape. "It was a revolution, both technologically and culturally," Marsden insists. "It was a coincidence of technology, politics and skills." From the Elizabethan era, Falmouth mushroomed out of its marsh, a boom town in a void. Marsden compares the port to a colony itself, a magnet for incomers drawn to its sudden wealth. "It was open ground, a long way from anywhere... Everyone was a newcomer."

The writ of monarchs and magistrates ran very faintly on this coast. Falmouth's past sails down that narrow and disputed channel between criminality and enterprise. Piracy flourished here, as did its slightly more respectable cousin, privateering. Marsden tells his history through biography, with no local lives more redolent of wind-lashed illegality than those of the Killigrew family. Pirate kings of Falmouth in the 16th and 17th centuries, they were prone to sudden fits of loyalty to the crown, then equally abrupt hoistings of the Jolly Roger.

"What does the sea do to individuals?" Marsden wonders. "What does the sea do to communities and countries? One of the things, perhaps, is that it gives this extraordinary licence to people – the sense that they can get away with it." He then backtracks and finds this schema too "deterministic". But his book crawls with chancers who got away with murder. Hollywood romps, building on a tradition of jingoistic romance, have sanitised the pirates. Marsden's account of early Falmouth shakes the stardust from a bloody business.

Over time, the explorers began to rival the brazen ruffians. Among the curious fortune-seekers who set sail from Falmouth in the 17th century, Peter Mundy travelled more than 100,000 miles and watched the Taj Mahal go up. Then came the naval heroes. In their front rank was admiral Edward Pellew – superior in seamanship to Nelson, some said – who unwisely returned from jousting with Napoleon's fleet to farm for a while. After the thrill of the sea, watching crops grow "made his eyes ache".

Come the 19th century, and Falmouth-based reformers who wanted to amend the world took over from the brigands who sought to plunder it. James Silk Buckingham, teetotal anti-imperialist and anti-slavery activist, counts as Marsden's favourite among this high-achieving crew. He survived successive captures and rescues to blaze a highly moral trail across the Ottoman empire, Persia and India.

To Buckingham we owe the fullest account of the most remarkable "blow-in" who crossed oceans to make Falmouth – strategic base of the Royal Mail's packet boats from 1688 to 1850 - their home. Joseph Emidy, a brilliant musician and composer born in west Africa, found himself pressganged in Lisbon in 1795 to serve as fiddler on Edward Pellew's ship, the Indefatigable. Already a freed slave, now captive again, he was released from the navy in Falmouth. Forr many years, he led the town's musical life as both performer and impresario. He wrote concerti, quartets and symphonies that won the esteem of colleagues of Haydn and Beethoven. Yet not a single note by Emidy – not only Cornwall's but Britain's first African-origin musical celebrity – has, so far as we know, survived.

The Levelling Sea rides high on a tide of such tall tales – all of them true. As Marsden came to maturity as a writer, he learned from a glittering generation of non-fiction narrators: the likes of Colin Thubron, Bruce Chatwin and Jonathan Raban. More recently, the "new nature writing" of authors such as his friend Robert Macfarlane, Kathleen Jamie and Richard Mabey has offered another kind of inspiration: "I find myself responding to that directly myself, but it has also thrown up some really wonderful writing, with the weaving-in of history and place."

Although he allows that fictional and factual prose share "devices and techniques", he emphasises that authors of the latter have to honour the line between them as one of the "pillars of writing". They simply mustn't make things up. For Marsden, "There's an unwritten contract between the reader and the writer. The reader relies on that contract... And if you breach that contract as writer – and I've seen it – then you're destroying everything that you've created. I have seen the fury of readers who have been hoodwinked like that. It's like someone has played a joke on them... Every book has its own rules and you have to be clear about what they are."

Savoury legends about the exploits of Lady Jane Killigrew, reputedly a pirate herself, lurk in the Falmouth records. Alas, they are fantasies. "As a writer, you think, 'I've lost that – how annoying'. And yet what you do find is much more interesting, if less colourful, because it's true. Something that has happened does have a quality about it." Marsden mines drama and colour enough from the hunt in the stacks for precious nuggets of fact that will bring a person or place to life: "All my books have been about finding the story as much as the story itself." The Levelling Sea does contain one well-sourced hint of pirate treasure buried somewhere near Falmouth. (Where exactly? Read it!) Yet the real gold, as it shows, hides among those dusty shelves.

Marsden's next literary trip will stay close to home but take him inland, for a book about Cornwall's mysterious antiquities and the "layers of interpretation" they have attracted down the centuries. Noting that "All the books I've done have been about people whose lives have been shaped by place," he points out that even the Neolithic builders of stone circles may have conceived of their henges and menhirs as a creative response to the spirit of the landscape. On the coast or in the country, nature can still drive culture.

Early in his career, Marsden talked to elderly exiled Armenians. They mourned not only the massacres of their people during the First World War but expulsion from a cherished home. "What was consistent, it seemed, was that the loss of the land was a greater wound than the loss of the population... A lot of our culture is based on place and landscape - much more than we now acknowledge."