Along the great divide

It's true, it doesn't sound like a rest. The terrain is rarely flat, mostly undulating and sometimes plain steep. The weather is also a lottery. This is Wales after all, celebrated for its well irrigated mountains and valleys.

Although the larger part of it is now in Wales, it also bisects three English counties. If, like me, you're half Welsh - and there are a lot of us throughout the English-speaking world - it's a good chance to think about belonging, roots and your ancestral connection to this small but perfectly formed country. When you've 10 hours a day to fill, this is handy. In my case, my girlfriend has kindly agreed to keep me company.

Coming in the opposite direction we will meet several solitary walkers, all of them committed-looking men in their 30s or 40s, lugging rucksacks the size of coracles.

With our laden rucksacks (though companies can organise your luggage to be sent on to your next bivouac) we set off and, for the next three days, lose sight of Offa's Dyke altogether. Why? Well, the twisting river Wye formed one natural boundary, the dense ancient woodland in Monmouthshire another. And it seems the southern route of the path was less disputed than the land further north. And then there are the Black Mountains, which form an unarguable rampart.

People sometimes snigger at the dyke's size, the way they do at Hadrian's Wall, the ankle-high structure built to hem the Picts behind a northern barrier. ''The traveller would pass it unheeded if not pointed out,'' sniffed one writer in 1803. ''All that remains is a small hollow which runs along the cultivated fields, perhaps not eighteen inches [45 centimetres] deep in the centre, nor of more than twenty yards [18 metres] width.''

In places the boundary is indeed not much to look at. But 1200 years on, at other points, it still very much is. Offa's engineers took care to heap the earth up from the Welsh side, so at its highest points a Mercian on the dyke would have stood up to five metres higher than a Welshman in the neighbouring ditch. It runs more or less uninterrupted across 128 kilometres of variable terrain, across flat lands and up half-vertical slopes. Hikers - or dykers, as we start referring to ourselves and others we encounter on the path - are left in no doubt: it is an astonishing achievement.

It must be admitted that the pleasure comes with a bit of pain. We bite off more than we can chew on a spectacular day one - 35 strenuous kilometres including navigation errors - and can barely move the next day as, with aching muscles and bags apparently laden with rocks, we cross the sunny fields of the Vale of Usk.

Day three is another 32-kilometre slog: over a ridge of the Black Mountains to Hay-on-Wye, home to the biggest collection of second-hand bookshops in the world. The clouds clear and we can see for miles, though not as far as from the top of Hergest Ridge on day four: much of Offa's old kingdom of Mercia, the twin peaks of the Brecon Beacons and other Welsh summits.

By this time we've entered Wales and left it again. On day five, when we re-enter the land of my fathers between the easily confused border towns of Kington and Knighton, it starts to rain. This is when we realise we should have invested in leather footwear.

The rain itself lends lashings of atmosphere, and the rest of us remains amazingly dry, but for three nights running we are stuffing Gore-Tex boots with newspaper. Hey, at least we aren't camping, unlike one disconsolate couple from Pontypool we meet: they are sheltering under a tree, soaked to the skin and shivering.

South to north is the more popular option. The prevailing wind is at your back, which keeps the rain out of your face. Should it deign to put in an appearance, the sun's not in your eyes either. And it should be said that sun is a frequent visitor. We have one blissfully bright morning walking along the upper reaches of the Severn. And, in the second half of the walk, the weather forecasts predicting biblical deluge are consistently wrong.

The northward trek also provides a more rousing finale as you head over the punishing Shropshire hills, on towards the spectacular mountains above Llangollen and the final push across the heather-clad Clywdian range. From up here we can see all of Snowdonia, jutting importantly to the west, and the spread of Liverpool and Merseyside to the east. On an even clearer day you can also see the Isle of Man and even the Lake District.

Our companion throughout is this persistent rib of earth driving across the landscape. The dyke is surprisingly full of surprises. What was once an instrument of oppression now has bushes sprouting from it, hedges, fences, hawthorns and huge oaks, even exotic mushrooms and polka-dotted red toadstools. Sheep and cows graze on it, badgers and rabbits burrow under it. When the dyke and the path part company with a couple of days to go, it's as if we are saying goodbye to an old friend.

Plants are not the only thing to have sprung up along Offa's Dyke. The path was opened in 1971 and there are moves to have it anointed a UNESCO World Heritage Site. That might not be popular with the few farmers who refuse access to it but it'll be popular with the array of bed and breakfasts now lining the route, most of them as plush as the several good hotels in the bigger towns. We eat excellently, too.

Offa's Dyke Path offers pretty much everything: sea, rivers and mountains, sun, rain and wind, mediaeval churches, bristling castles and monastic ruins. A word about the latter. It's on the first day that we come to a pragmatic conclusion. Walking along a high-ish escarpment through old forests we come to a glade where, through a clearing between trees, there is a distant prospect of Tintern Abbey. None of us has ever been to Tintern. The roofless ruin, once the mother house of the Cistercian order of monks who spread through Wales in the 12th century, beckons seductively in the flat bright light. However, it's more than a kilometre off the route. We can go another time. Preferably by car.

And besides, there is more than enough to see in the unfolding drama of the landscape. Offa's Dyke passes, not unnaturally, across the terrain where the contrasting topographies of England and Wales meet: flat land and mountain, the horizontal and the vertical. To walk along the path is to listen to a kind of unfolding dialogue.

And what of the final push, the murderous last kilometres? We do another 32-kilometre walk to finish. Prestatyn is not perhaps the prettiest town to greet you when your feet are killing you as never before. But so what? Completing the walk gives me a feeling of well-being and satisfaction I've never previously had from a holiday. You can go more slowly than we did (or, if you're so inclined, faster). You can do it in stages or at any time of year.

Even in summer, you'll be mostly alone as you listen to the rumbling echoes of history.

Jasper Rees walked along the Offa's Dyke Path courtesy of Visit Wales.

FAST FACTS

Getting there

Qantas has a fare to London for about $1940 flying to Singapore (about 7hr) and then to London (14hr). This fare also allows travel via Bangkok and Hong Kong. Fare is low-season return from Melbourne and Sydney, including tax.

Walking there

It's possible to walk the Offa's Dyke Path in all seasons but the ground is less soggy in summer.

Companies that organise walks include Celtic Trails (www.offasdyke.com), Contours Walking Holidays (www.contours.co.uk/) and Drover Holidays (www.droverholidays.co.uk). Depending on the length of the trip, prices vary from about £800 ($1300) to £1000 a person. For more information from the Offa's Dyke Association, see www.offasdyke.demon.co.uk.

Staying there

If organising the trip on your own, staying in the following places is recommended (they are listed south to north). Some provide evening meals and all will provide packed lunches. Prices for a double room range from £60 for the cheaper bed-and-breakfasts to £110 for the smarter hotels.

The Hendre Farm House, near Monmouth: a well-appointed B&B (www.thehendrefarmhouse.co.uk).

The Old Rectory, Llangattock Lingoed, near Abergavenny: comfortable, old-style B&B (www.rectoryonoffasdyke.co.uk).

The Swan, Hay-on-Wye: grand, old-fashioned county hotel (www.swanathay.co.uk).

Arrowbank Lodge, Kington: friendly riverside B&B (www.arrowbanklodge.co.uk).

Milebrook House Hotel, Knighton: country-house hotel with excellent restaurant (www.milebrookhouse.co.uk).

Little Brompton Farm, near Montgomery. Rustic B&B (www.littlebromptonfarm.co.uk).

The Royal Oak Hotel, Welshpool: big, busy county hotel (www.royaloakhotel.info).

Lynstead Lodge, Trefonen: friendly B&B (www.lynsteadlodge.co.uk).

Cornerstones Guesthouse, Llangollen: riverside guesthouse (www.cornerstones-guesthouse.co.uk).

Manorhaus, Ruthin: glacially cool hotel with superb restaurant (www.manorhaus.com).

Reading

The Offa's Dyke Path: Walking Guide to the National Trail by David Hunter (Cicerone, £12.95).