About 750AD, Offa, King of Mercia and overlord of the greater part of England, decided to dig a ditch, or dyke, some 290km long, marking the border of his kingdom with Wales.
Why Offa wanted to construct such a huge earthwork, which in places measured 6m from the bottom of the dyke to the top of the earthen bank, is unclear.
The general assumption is that he was trying to hinder incursions by the Welsh into his territory, but some believe that he simply wanted to leave a monument to himself.
Whatever the reason, his labours have resulted in the creation of the Offa's Dyke Path, a long distance National Trail of 284km traversing the border country between England and Wales.
The path follows the original line of the dyke in many places, where even after 1200 years, the earthwork is still clearly visible.
In others it takes diversions to traverse more scenic routes, which results in a trail that passes through varied and beautiful countryside, sometimes remote and wild, at other times pastoral and serene.
The route of the path has been designed to cater for walkers of all abilities.
There are plenty of steep gradients for those looking for a physical challenge, and the track passes through, or close to, a number of historic towns and villages, which means that the distance to be walked each day can be adapted to a walker's level of fitness.For those seeking a gentler passage a number of circular trails lead off from the main path, allowing comfortable day-walks to be undertaken.
Our journey begins on the cliff top at Sedbury, high on the northern bank of the Severn River, where Offa began his epic task. The dyke is clearly visible here, running down steeply between the trees from the top of the cliff.
There are two rivers of significance on our journey, the Severn and the Wye.
Both rise in the Welsh Cambrian Mountains and flow independently until the Wye enters the Severn Estuary at Chepstow, the first town on route.
The first stage means following the Wye to the historic town of Monmouth, but this is no stroll along a flat valley.
A long sharp climb through beautiful bluebell woodlands is followed by a series of switchbacks high above the river, leading to a superb view of the ruins of Tintern Abbey, which date from 1131.
This is the first structure which induces a feel of the history of the land through which the path winds, from stone circles, Iron Age forts, ancient castles and churches and remnants of the Industrial Revolution.
The Wye is in spate, following the huge amounts of rain that have fallen over the previous weeks, and the brown water is surging along, carrying large chunks of timber and leaping in high, dirty, frothy waves against the piers of the bridges as I near Monmouth.
The weather is cold and windy but thankfully dry, and so it would remain for the next eight days.
I'll pause here to mention those all important aspects of a walk of this nature; accommodation, food and drink. I've walked with just a day-pack, having my luggage moved ahead, and am staying in B&Bs, pubs and farmhouses, all of which are excellent.
As ever, the great 'full English breakfast' provides fuel for the walking day and the image of a pint (or two) of cool amber liquid keep the feet moving for the final kilometres of the day.
Monmouth to the little village of Pandy is the introduction of the two 's-words' of the walk; stiles and sheep. There are more sheep than stiles, but you don't have to climb over the sheep.
I am told that there is an intention to replace the stiles along the way with kissing-gates, of which there are a number early on.
This section also includes a number of picturesque villages, including Llanfihangel Ystum Llywern, one of the many unpronounceable placenames I encounter.
One really good thing about the walk is the way marking or signposting.
The path was set up in 1971 and much of the original marking has been retained, and augmented with newer markers.
It is almost impossible to get lost. Carved wooden signposts either show the full name of the path or bear small round markers with yellow arrows on a white background with the logo 'Offa's Dyke Path'.
In all cases the path is also marked with the 'acorn' logo, the symbol of the National Trails.
From Pandy to Hay-on-Wye the route turns into wilder country, as the path crosses the Black Mountains, steep bracken covered slopes leading to wild moorland and black, peaty bogs.
This is a tough, bleak section, with a steep climb out of Pandy followed by a long stretch along the ridge to Hay Bluff, the highest point of the whole trek at 621m.
The boggy area has been paved with a long pathway of large flagstones and is well marked with posts and rocky cairns. The cold, clear weather allows superb views of long, narrow valleys dotted with isolated farms but the strong north wind, blowing straight into my face, discourages standing to admire them for more than a few moments at a time.
The ridge walk is followed by a steep descent through more sheep filled meadows to the small town of Hay-on-Wye, famous for its castle and its many outdoor bookshops.
I am joined here by two friends, Mike and Debbie, who are to walk the next two sections with me.
A few pints of well earned Welsh bitter at the Blue Boar pub, a good night's sleep followed by the inevitable 'full English' breakfast sees us rearing to go the next morning on a shortish section to the old market town of Kington.
This is a relatively comfortable walk with the path initially following the Wye and then climbing steadily to pass over Disgwylfa Hill and Hergest Ridge before a long, easy descent into the town.
The airy slopes of the green moorland and the soft grass underfoot, together with the welcome appearance of the sun, make this a beautiful day's walking.
This is 'drover' country. Droving is the practice of moving livestock over large distances by walking them 'on the hoof', and for many hundreds of years the drovers pushed their sheep and cattle, at a speed of about 16km a day, through a myriad of narrow lanes and across open moorland to the markets of towns such as Hereford and Shrewsbury.
About 3km beyond Kington, the path returns to the dyke itself, and remains with it (and indeed in places on top of it) for some considerable distance.
This stage of the walk takes us to Knighton, deep in the Teme valley and home to the Offa's Dyke Association.
This is true border country where it is difficult to be sure if you are in Wales or England. It is said that in times gone by the penalties for being caught on the wrong side of the dyke were severe; the Welsh had their ears cut off and the English lost their lives. We three are all English but if things become difficult I'll shelter behind my Australian citizenship.
The descent into Knighton is long and steep.
"It looks like a long way up for you tomorrow, mate," Mike says.
He was to be proved right, but the good amber liquid and excellent food in the Knighton 'Horse and Jockey' assuage my fears.
I make the tough walk out of the valley accompanied by another friend, John, and we continue over some demanding terrain, to the B&B at Caemwygal Farm, north of the town of Montgomery.
The dyke is very much in evidence as the path passes through farms and meanders through woodland and over hills, with some very steep ascents and descents, until it finally levels out near Montgomery.The sun is shining and the views at times are breathtaking. It is in this section, on Llanfair Hill, where the dyke reaches its maximum elevation at about 430m and also where the path reaches its halfway mark.
It is here that I lose my way for the first time and have to backtrack nearly a kilometre.
It's entirely my own fault as I have missed a perfectly obvious 'acorn' symbol. The dyke is lost again now as the path descends and follows the line of the River Severn, across flat meadow land (stiles and sheep) for just under 5km, before turning to follow the towpath alongside the Shropshire Union Canal.
The sheltered walk along the towpath is blessed relief from the cold north wind that has been blowing icily into my face for most of the day and its resident swans provide some peaceful company and photographic opportunities.
Then it's back to the banks of the Severn, where the path rejoins the dyke once more, followed by a second walk along a towpath, this time along the Montgomery Canal, into the village of Llanymynech and the welcome hospitality of the Bradford Arms Hotel.
Llanymynech ('Church of the Monks') straddles the present border between England and Wales, with its eastern half in England and the western half in Wales.
Quarrying has been an industry in the area for centuries and the town is dominated by a huge limestone quarry, now defunct.
Quarrying seems to have destroyed sections of the dyke in this area and it only becomes reunited with the path at Froncysyllte, some 29km to the north.
After a series of cold and windy, albeit dry days, the weather gods desert me. The next morning dawns grey and drab, with a strong smell of rain in the air.
The route is to the town of Trevor, a walk of just over 30km through quiet lanes and fields. All is well for the first couple of hours although ominously the wind has dropped for the first time in a week.
Then the heavens open, the wind picks up and I'm treated to a delicious mixture of rain and hail.
Raingear on, I bury the camera in the backpack. A fairly comfortable walk is made much harder in the downpour.
There is a fascinating twist to the passage of the Offa's Dyke Path as it enters Trevor, where two options are on offer.
Thomas Telford, born 1757 and arguably the greatest engineer of his day was commissioned to build an aqueduct that could take boats across the River Dee.
This structure, completed in 1805, stands 36.5m above the Dee and supports an aqueduct more than 300m long. Walkers are offered the choice of walking across this amazing structure or taking the more comfortable path underneath it. Don't try it if you suffer from vertigo.
Sadly the last two days of the walk are to be dominated by atrocious weather.
It's a shame, because the next section between Trevor and Clwyd, crossing the Clwydian Ranges, although quite remote, is said to offer some beautiful views.
The terrain is certainly up and down, but the gradients are not steep and boardwalks carry walkers over boggy areas early on.
The final section is a comfortable, if very wet walk following lanes and field paths into Prestatyn, through the Nature Reserve, and thence to Offa's Tavern, to raise a glass to the ancient King of Mercia.
So, to sum up, Offa's Dyke Path is an excellent walk, traversing beautiful countryside, offering varying degrees of difficulty with regard to the distance walked each day and providing excellent choices of accommodation, food and drink along the way.
The weather will always be a factor, but that, especially in the UK, is a risk all walkers have to take.The highlights for me are the flora and fauna; birdsong everywhere from the dawn chorus, blackbirds singing their hearts out in the woods, skylarks singing high above the moorland and even a nightingale in Monmouth.
Added to this is the friendliness of everyone along the way, especially the hosts in the pubs, farmhouses and B&Bs.Author's note: Thanks are due to Northwest Walk, who organised my itinerary with their usual efficiency, to the Offa's Dyke Association who have done so much to promote the path and to all those who are responsible for the way marking. Thank you all.