For the first time in 1,600 years, it's possible to walk - on a new national trail - the entire length of Hadrian's Wall. But is it worth the hike? JANET STREET-PORTER follows in the footsteps of the legionaries who kept watch on the edge of the Roman Empire

Walls are emotive structures - and none more so than the extraordinary feat of engineering masterminded by the Roman emperor Hadrian over three years, starting AD122. In order to separate his province in southern Britain from un-Romanised tribes in the north, he built a 73 mile-long wall, 15ft high and up to 10ft wide, marking the border from the Tyne in the east to the Solway Firth in the west. It did the trick: Hadrian's Wall did not succumb to the enemy until the collapse of Roman Britain in the early 400s. It then fell into disrepair and, as a source of prime building material, was extensively looted for farmsteads along its length. In 1754, in a breathtaking piece of vandalism, a new road to Carlisle (today's B6318) was simply built on top of a large section.

Hadrian's Wall was designated a World Heritage Site in 1987, and, last month, an 84-mile national trail was opened that loosely follows its route. The only army on patrol these days is clad in waterproofs with plastic map holders flapping in the stiff breeze. For four days, I joined them.

DAY ONE: Wall to Housesteads

I am dropped outside a village called (not very imaginatively) Wall, by David from Contour Walking Holidays. I'm trudging what Contour describes as "the best of Hadrian's Wall", taking four days to get to Carlisle and missing out the first part of the trail from Wallsend and out of Newcastle-upon-Tyne via the waterfront. As we drive from Newcastle station I spot my first glimpse of Hadrian's handiwork by a dual carriageway. A lot of this early part of the route follows roads, albeit minor ones, and it's hard to imagine the lot of the lonely Roman soldier as four-wheel-drive vehicles and tractors whizz past at 50mph: these are very straight, very Roman roads.

It's a northern kind of day, with a stiff breeze blowing and a lot of grim, grey clouds massing on the horizon. I pass my first turret at Brunton, just before Chesters Bridge, a pretty stone structure over the Tyne. The ruins of the Roman bridge lie to the west. I decide to stop and visit Chesters fort, which is very impressive, with a bath house containing rooms for "alternative treatments". But I'm even more knocked out by the museum, which is crammed with all sorts of treasures. As I stop to write in my notebook, I can't help noticing a fellow walker's leg sporting an elaborate Celtic tattoo up his calf.

Back on the main road and up a hill into Walwick, with its solid stone houses and a stagnant cattle trough, then up a lane past foxgloves and on to my first bit of footpath away from traffic - hoorah! The local farmer obviously hates walkers as there's a brand new "Bull in field" sign by the footpath and "No unauthorised persons" signs on either side of his driveway. Meanwhile, fighter jets roar a few hundred feet overhead on their way north to play war games over Keilder forest. On my first stretch of exposed Wall, I meet a man from Newfoundland in thick blue cotton gloves, a wide-brimmed Tilley hat tied firmly under his chin, and dark glasses (it's almost raining). He has a white flowing beard and matching long hair and, before long, he's telling me how he plans to return and walk the bit between Carlisle and Bowness, so that he "has closure". Very New Age.

After a drab straight stretch (and lunch huddled between cowpats in a ditch out of the wind), at Carrawburgh I encounter tattooed-leg man at the temple of Mithras, by the fort of Brocolitia. The Roman name has nothing to do with the cancer-fighting green veg, but derives from the Celtic for "badger holes". Either way, it's a windswept bog.

I plod along by the road in lashing wind and rain. Soon my legs are soaked and the damp has crept up to my knickers. I forgot to say I heard skylarks and curlews earlier; now they're all sheltering from the elements. Even the cows have huddled under the few trees available. At Sewingshield Crags I make a detour up a steep slope to the white trig point for fantastic views stretching away at least 10 miles to the north, beyond the waters of Broomlee Lough, and south, over Allendale, to Weardale. This is where I walked with Sting in 1998, part of my potty straight-line route from Edinburgh to London for a television series. It was pouring with rain then. This is my first taste of the up-and-down switchback of the next few miles, where the Wall excitingly wiggles over sheer drops and rocky crags.

At Housesteads fort you buy tea from a kiosk outside in the wind and rain and drink it inside the gift shop. I suppose it's beyond English Heritage to come up with waitress service at this extremely popular spot. My legs are aching and I've only walked about 10 miles.

Marian of Contour meets me and says that Hadrian's Wall is their biggest-selling holiday at the moment; she reckons some 500 people are walking it during any one week. I soon discover that 500 people over 84 miles still means you more or less have it to yourself. But this popularity means there is a shortage of accommodation, until more farmers stop whingeing about walkers and latch on to the potentially huge source of income from bed, breakfast and evening meals.

I stay at the Centre of Britain hotel in Haltwhistle, which is friendly and comfortable. Dave, the owner, was part of a group of locals who relaunched the run-down town as the "centre of Britain" a few years back. Now the high street has restored shopfronts and the station looks terrific with its elaborate signal box and clean waiting-rooms.

DAY TWO: Housesteads to Walltown Quarry

I'm walking with my friend Jane today, and we start with a big debate about sticks: is it too feeble to use them? My knees are still aching from yesterday, so I pack the sticks. Mind you, last year in the Dolomites I managed to fall over my own sticks and cut my hands (don't laugh please). En route to the start, we are shown the Wall's most famous tree, proudly standing in a scenic dip, as featured in a scene in Robin Hood with Kevin Costner - or was it Mel Gibson in Braveheart? We were in the middle of discussing sun block and not paying too much attention. An arctic gale was lashing our faces, which were slathered in cream. We must have looked like a couple of pilchards.

I can really recommend Housesteads fort, which enjoys a breathtaking position on the brow of a hill. It was already full of school trips; some young men dressed as Eminem were chasing sheep and whooping while a group of American teenagers plaintively asked, "Is this something to do with 1066?" Here the Wall stands proudly restored, snaking up and down as far as your eye can see, and we spent a thrilling couple of hours clambering up and down steps and sheltering from the gale in the odd clump of trees. Everyone walking towards us claims we are "walking in the wrong direction". As my face has started to resemble a red pan rubbed with a scourer, I can see they have a point. (By the way, the official guide is written east to west.)

Over Hotbank Crags we toil, as a pair of swans paddle about on the blue waters of Crag Lough far below. We pass the ruins of milecastles and their defended gateways: between each milecastle there are also the remains of turrets in the most inaccessible spots. I try to imagine the lonely lot of a sentry listening out for the enemy and watching the horizon for camp fires. While most of the soldiers stationed on the Wall came from Germany, Gaul and Belgium, being stationed in chilly northern Britain must, nevertheless, have seemed like drawing the short straw.

At Steel Rigg, there is a sudden influx of unfit tourists, staggering up from the car park, video cameras at the ready. A little further on we lunch tucked between boulders by the trig point (345 metres) on Windsheild Crags - the highest point on the trail. This is walking at its absolute best, like riding a switchback - exhilarating and challenging. Through fields, the Wall seems to disappear into a series of undulating bumps before the final slog up Walltown Crags, where it rises a couple of metres. Five hours after we'd started, we gingerly make our way down to the car. An unforgettable 10 miles.

DAY THREE: Walltown to Walton

The day starts sunny, with thankfully little wind. In the main street of Haltwhistle, however, a storm is brewing. The Women's Institute fair is underway in the market place, but the cake stall doesn't plan to open until 10am. A disgruntled group of bun and sponge purchasers waits anxiously. A potential disaster, when my taxi driver drops me off at the wrong quarry (more than three miles further back), is averted after I accost Glyn, a physiotherapist, in the car park and beg him to give me a lift. I soon reach the scenic ruins of Thirwell Castle via a metal bridge over a burn, and then meet a group of burly blokes out on a 30 mile-long training "walk" along the main road. My first kilt of the trip!

Just before Gilsland, the path goes through a small vegetable patch decorated with plastic figures, from Snow White to Noddy. Dennis the Menace is guarding the gooseberries, the farmer tells me, because his sundial was stolen a few months ago. In Gilsland itself I walk through a front garden full of strawberries and leeks. The owners cheerily wish me good morning; everyone has been extremely friendly so far. Tacked to the outside of a wooden shed is a red and yellow plywood shield, with a plastic sweet jar underneath that contains leaflets advertising "Jeff's Roman Experience": "Younger members of the audience will enjoy trying on authentic Roman costumes." I must remember that for my next Christmas party.

A wonderful stretch of Wall west of Gilsland passes through a farmyard and downhill to Willowford Bridge, where the river has changed course and I can see the excavated remains of the original Roman bridge, now in the middle of a field. A climb up a steep bank takes me to Birdoswald fort (Camboglanna) and visitor centre just as the Cosmos tour bus arrives; its cargo busily snap the bit of Wall nearest the entrance.

From here on, the Wall passes through undulating pasture, leaving the bare grassy expanses of the moors behind. As I eat my sandwiches on a bank of the earthworks, a straggly group of hobbling adults approaches. They turn out to be American tourists with their own guide. "Tell me, Andrew," one asks pathetically. "How many cows are there in a herd?"

A long straight walk by the road along the back of a ridge reveals verdant fields. Through Banks (how many villages have you counted so far with names to do with the Wall?) and I am soon in the village of Walton. A sunny 10 and a half miles, much easier than yesterday.

DAY FOUR: Walton to Carlisle

My long-suffering partner Peter accompanies me on this 12-mile section and the day is hot and humid. The Wall seems to have disappeared as we walk past glossy cows and frisky calves. Absolute silence, a carpet of buttercups and daisies, foxgloves in the hedgerows, cool sections in small woods. Eating lunch near Carlisle Airport at Irthington, we see a succession of weird and wonderful flying contraptions chug into view. They sound like sewing machines and look like Jonathan Emmett drawings. Down a lane, we pass a sad abandoned farm and then cross over the A69, my first big road. The noise irritates me. After Low Crosby, we follow the bank of the shallow river Eden with patches of water lilies and, all too soon, get back on the road to cross over the M6 and (depressingly) follow a cycle track next to the road through Rickerby. Where's the Wall?

We're now on the edge of Carlisle, traversing parkland with a war memorial. We cross the river Eden via a steel suspension bridge to the opposite bank. It's Sunday afternoon and there's hardly anyone in sight. Cutting through the Debenhams shopping centre, we spy Carlisle castle, cars whizzing past. Through the subway and we make it to the castle ticket office just as it's closing. Never mind; I worked in Carlisle for six months making a series for Channel 4 and visited every interesting building in town then. Today has taken nearly five hours and I'm desperate for a bar of chocolate and a drink.

If you are interested in walking Hadrian's Wall, take my advice and stick to the "highlights". Doing the whole route just seems macho. If you want to walk coast-to-coast, Wainwright's route from St Bees Head in Cumbria to Robin Hood's Bay in Yorkshire is far more enjoyable. I'm glad that I walked from Carrawburgh to Walton, but I'm sad that my love affair with Hadrian had to fizzle out on a cycle path. Meanwhile, don't talk to me about turrets; I've stumbled past enough of the things to last a lifetime.

Janet Street-Porter's walk was arranged by Contour Walking Holidays, which also books self-guided walks on the coast-to-coast route. Contact Mark Townsend (01768 867539 or e-mail