Simon Garfield sets the tone for his paean to the dying art of letter writing by first quoting Goethe:

"We lay aside letters never to read them again, and at last we destroy them out of discretion, and so disappears the most beautiful, the most immediate breath of life, irrecoverable for ourselves and for others."

Anyone who has ever written or received personal letters, as opposed to emails, texts or tweets, will warm to Goethe's description. When Garfield posits the choice of "inbox or shoebox", many of us will think immediately of those packets of long-unread but still treasured missives, whose contents years later remain potent. Yet, valuable though the words themselves may be, the letter itself is possibly more important still. The writer may now be dead, or gone, but their personality leaps out from the hand-written envelope before the page is even opened. This, one of the most powerful and meaningful human arts ever devised, is a legacy we are swiftly destroying, in part through haste and convenience, but mostly, I suspect, from sheer laziness. Letters, even the briefest, require thought and care, and we gladly fool ourselves that we have too little time for either.

With the air of a man swimming against the tide, Garfield flings himself into his subject, arms and legs flailing against a current far stronger than himself. It is a noble venture, but one so vast in scope that his elegy for this once ubiquitous literary form cannot be anything but incomplete. What it need not have been is chaotic, but the helter-skelter mood and presentation of this work is perhaps eloquent of Garfield's passion for his subject, and his sense of urgency. At times a little dizzying, it is more like being eagerly shown around a rag and bone shop than conducted through the corridors of a rigorously ordered mind. And yet, haphazard and self-indulgent though To The Letter can at times be, it is also fascinating.

Garfield sensibly offers a chronological progression through the history of personal letter writing, from the flamboyant, formal Greeks, to the first true letter writers, the Romans. In dispatches from Pliny the Younger, for instance, one sees how tenderly he loved his wife, whose letters he pines for. Of more historic note is his depiction of Pompeii: "Many besought the aid of the gods, but still more imagined there were no gods left, and that the universe was plunged into eternal darkness for evermore ..."

For those who yearn to catch a glimpse of ancient times, Garfield offers a keyhole in the shape of brief but telling messages from Roman soldiers posted on Hadrian's Wall. Much though this reader loves Northumbria, one feels for these southerners, camped out in the inhospitable north: "My fellow-soldiers have no beer. Please order some to be sent."

Scampering across the ages, he traces the growing importance of personal correspondence, and with it the emergence of a postal service, first designed to ensure Henry VIII's letters, such as those to Anne Boleyn, reached their destination safely. Readers might be interested to learn that the postmaster general under Oliver Cromwell also held the position of spymaster general. Then, as now, private letters were opened if they were deemed to pose a threat to the state. Those wishing to evade prying eyes, however, learned to write between the lines with lemon juice, which, when warmed, was briefly visible before fading once more. The paranoid preferred orange juice, which remained legible after warming, thus warning the recipient that their message had been intercepted.

In less treacherous times, the arrival of the postage stamp, and of Anthony Trollope's famous red pillar boxes, changed the fortunes of letters forever, bringing them within reach of everyone who could write and afford a stamp. Shortly after the Penny Black was issued in 1841, it was observed in Punch that a new breed of collector had been born: "they betray more anxiety to treasure up the Queen's heads than Henry the Eighth did to get rid of them."

Demonstrating the seriousness with which letters were treated is Garfield's account of America's famous Dead Letter Office, in which 19th-century officials displayed near-telepathic imagination in deciphering illegible handwriting or misdirections, or finding a home for letters optimistically addressed, as this one was, "To my Son he lives out West he drives a red ox the rale rode goes By Thar".

Bringing his narrative up to date via the letters of Jane Austen (prosaic), Emily Dickinson (embarrassing), and Virginia Woolf (neither), Garfield darts hither and thither across the field of letters like a hound distracted by too many tantalising scents. There is, however, one constant thread throughout this work that holds it steady and provides a moving and illuminating insight into a world that will soon be far from our own.

Interspersed between chapters are letters sent by one Signalman Chris Barker to a friend, Bessie, with whom he'd worked in the London Post Office before being conscripted in the Second World War. Over months and years, writing from Egypt, Italy, and Greece, Chris's relationship with Bessie grows from platonic to passionate, during which she ditches her boyfriend. The unreeling story of his war and hers, the slow realisation that they are in love, and the way this is expressed, is truly touching. It also shows how letters can irrevocably change lives. Katherine Mansfield once wrote: "This is not a letter but my arms around you for a brief moment." Are we really going to let something this important disappear for ever?