It is the longest linear earthwork in the UK, and one of the longest in Europe, stretching for 177 miles (285km). The modern boundary between Wales and England closely follows much of the route of the dyke.

The discovery by Clwyd-Powys Archaeological Trust now dates the earthwork to the second half of the 6th century.

Despite this new revelation, the Trust says, “Further work is needed on other parts of this enigmatic monument before we can really say who built it and why" - which leaves the door (and ground) wide open to more expansive theories behind the dyke’s creation.

In places the dyke is 88ft (27m) wide and 8ft (2.4m) high. It is scarcely believable that such a huge earthwork could have been created by human hand without the aid of mechanical earth-moving equipment.

So, what if it’s not a monument at all? And the question is not who built it, but what (and how)?

Siôn Griffiths obviously had the same thought and got in touch with an intriguing new avenue to research;

@evilshemp “it's clearly made in prehistoric time by a 'Graboid' that lived in Wales #Tremors”

Clearly it is, but prehistoric? This didn’t seem likely, as the earliest known film of the terrifying subterranean creatures only dates back to 1990.

However, some initial research revealed a graboid (Caederus, C.americana) fossil was thought to date from the Precambrian Eon (source: Tremors 2).

Until it was realised no life existed on land then.

The date of the fossil was subsequently revised to the Devonian period, during which time prey large enough to sustain the gigantic terror worms would have existed.

This geologic period ended some 360 million years ago, long before the new earlier date of 430 for the creation of Offa’s Dyke.

So, the timeline still fits. Graboids could have created the dyke in prehistoric times.

But Griffiths then appeared to cast doubt on his own theory; @evilshemp: “Would the soil in Wales facilitate their movement? As most of their sightings have been in dry landscapes”

This could be the deciding factor. Graboids are a sandworm, so could they thrive in wet Welsh soil?

The British Society of Soil Science seemed to think not;

@Soil_Science "#soil of Wales might put your Graboids off, certainly would stunt their growth and limit movement!"

It’s true that graboids need loose soil to ‘swim’ through.

But this wouldn’t be the first time a non-native subterranean beast has been found on the western side of the dyke.

Which leads onto an even more chilling possibility – what if graboids have mated with the alien flesh-eating ghost slug (Selenochlamys ysbryd), creating an almost invisible hybrid?

That would certainly explain the current lack of sightings of graboids in Wales.

Spotted evidence of graboid activity in Wales? Could any other famous landmarks have been created by the creatures? Let me know in the comments below or via #WelshCryptozoology and I'll do my best to research any sightings. Possibly.

It is an impressive stretch of water but while it may be long, the lake is certainly not deep – going down to a mere seven metres at its deepest point.

Giraldus Cambrensis wrote about the lake in his book about journeying through Wales in the late 12th century, reporting the local tradition that the birds in the area only ever sang for a truly Welsh prince or ruler.

Giraldus also said the lake was often called Clamosus, which is the Latin word for 'noisy'. Whether or not he was thinking of the clamour of the singing birds when he wrote the words is not known.

Giraldus did, however, note that when the sheets of ice that invariably covered the lake in winter finally cracked, there was a loud noise. He may well, therefore, have had this noise in mind when he gave the lake its Latin name.

Quite apart from anything else, Llangranog Lake is remarkable for the fortified house or dwelling place on the lake, the only known example of a crannog in Wales.

The house on the lake

As this 'house on the lake' was one of several royal houses belonging to the rulers of Brycheiniog – palaces would be too grand a term – it does provide strong evidence of the links between Ireland and this part of Wales in the period between the rule of Rhodri Mawr and the arrival of the Normans at the end of the 11th century. Ireland has many examples of early crannogs.

The crannog at Llangorse, in effect an artificial island, measures about 40 metres in width and is situated 30 or 40 metres off the northern shore of the lake. Now it is covered in trees, bushes and reeds - a far cry from how it would originally have looked - and dates from the end of the ninth century.

Timbers from the wooden palisade that used to surround the island have been dated to come from between 889 and 993 AD but as several of these pieces of wood had been used on earlier buildings it is hard to be too precise with dates.

The island was built using oak planks as piles, sharpened at the bottom and driven into the floor of the lake. Then huge boulders, sandstone in the main, were used to fill the open space inside the piles. Small stones were  scattered over the boulders in order to provide a level floor and a strong wall of timber stakes erected to form a defensive palisade. A causeway, again made of timber, led to the shore on the northern side.

Quite possibly the King of Brycheiniog sent his craftsmen across to Ireland to learn the skills required for such a construction. If the lack of other, similar buildings in Wales is anything to go by, it was certainly something outside their experience. The other possibility is that one of the Irish builders may even have journeyed to Wales to advise on the project.

It is not clear what buildings stood inside the palisade but there would certainly have been a central or main hall. This was not the dwelling place of some local chieftain but one of the many homes of the rulers of Brycheiniog. The presence of a hall where they could live and entertain guests, where the bards and musicians could play and sing, would have been essential.

There were other smaller buildings where food could be cooked and servants could sleep. Finds during excavations on the island have included combs, glass rings, pieces of cooking pots and whetstones for the sharpening of knives and axes. They certainly indicate that this was a substantial settlement that was well used by the kings of Brycheiniog and their courts.

The various kings of the time – and Brycheiniog would have been no different – probably lived something of a peripatetic lifestyle. They would move between one royal house and another, collecting tributes and dispensing justice amongst their subjects. Therefore a substantial house or fortress such as Llangorse crannog would have been essential.

It is unlikely that a crannog like the one at Llangorse would have been occupied all year round although the king would have retained servants in the immediate area, to oversee his affairs and prepare the crannog when he next decided to inhabit the place. It probably provided a fair degree of employment, of one sort or another, for the people of the immediate area.

The demise of the crannog at Llangorse is a little unclear. Relations between Alfred the Great's English territories and Brycheiniog deteriorated in the wake of Alfred's death and in 916 AD Aethelflaed, the daughter of Alfred, sent an army into the Welsh kingdom. A number of burnt timbers have been found in the crannog and it is possible that the island was attacked and its defenders put to the sword by the English army.

Certainly the crannog was never rebuilt by Twedwr ap Elisedd, the ruler of Brycheiniog at the time, and in due course Brycheiniog became part of the kingdom of Deheubarth. What is left is an amazing archaeological site, the only known crannog to have yet been discovered in Wales.

Stonehenge

The excavation project of the tomb has been led by Professor Geoff Wainwright and Professor Timothy Darvill, who believe that the giant stones were brought from the Preseli Hills in Pembrokeshire to the Wiltshire grounds.

Prof Darvill said: "It's a little piece of keyhole surgery into an important monument, but it has actually lived up to our expectations perfectly."

Prof Wainwright added:

"The important thing is that we have a ceremonial monument here that is earlier than the passage grave.

"We have obviously got a very important person who may have been responsible for the impetus for these stones to be transported.

"It can be compared directly with the first Stonehenge, so for the first time we have a direct link between Carn Menyn - where the bluestones came from - and Stonehenge, in the form of this ceremonial monument."

The excavation will feature in the new series of BBC Two's Digging For Britain, which begins at 9pm on Friday 9 September. Louise Ord, an assistant producer on the series, has written more about the excavation on the BBC News website.

Eddie Butler at a handball court in Wales

In tonight's Hidden Histories, Eddie learns to play handball at Nelson's unique handball court - the only one in the UK.

Interior View of St Nicholas Church, Grosmont © Royal Commission on the Ancient and Historical Monuments of Wales

Professor Ralph Griffiths, Richard Suggett, and Rev. Jean Prosser talk with Eddie about the significance of Grosmont and the Norman conquest of upper Gwent.

Pantyrhwch cottage after restoration © Royal Commission on the Ancient and Historical Monuments of Wales

The team take a look around a farmhouse in Ceredigion where the owner's contemporary lifestyle happily coexists with the craftsmanship and planning of the old house.

They teams also meet 3D artist Iwan Peverett who developed a series of computer-generated reconstruction animations about Bardsey Island, which allows people to see how the "island of 20,000 saints" has changed over time.

The Royal Commission on the Ancient and Historical Monuments of Wales have created excellent, in-depth guides to each subject featured in tonight's programme. Read the guides on their website and view images relating to Hidden Histories on their Flickr photostream.

Hidden Histories, Thursday 27 January, at 7.30pm on BBC Two Wales.

Sakyamuni Buddha, Xiaofowan(AD1174-1252). © Dazu Rock Carvings Museum, Chongqing, China

The steep hillsides of the Dazu World Heritage site near Chongqing contain an exceptional series of rock carvings dating from the middle of the seventh century and developed between the ninth and the 13th centuries.

Head of Sakyamuni Buddha (AD1127-1279). © Dazu Rock Carvings Museum, Chongqing, China

The carvings comprise 50,000 figures in total, and are remarkable for their aesthetic quality, their rich diversity of subject matter, both secular and religious, and the light that they shed on everyday life in China during this period.

It contains superb examples that have become detached from their original setting, along with accurate replicas of some of the most important sculptures still in situ and dramatic large-scale images, to give some idea of what it is like to visit these spectacular places.

Stone carving being delivered to the museum

Speaking about the carivings, David Anderson, director general of Amgueddfa Cymru - National Museum Wales Director said: "Dazu rock carvings are some of China's greatest cultural treasures from a golden period of Chinese art.

"Hosting their first appearance outside of China is a privilege not just for the Museum but for Wales. I am confident this will be a popular exhibition and hope this is the beginning of a successful relationship between us and the Chongqing Culture Bureau."

Stone carving being delivered into museum building

Li Fangyin, curator of Art Museum of Dazu Rock Carvings in Chongqing, commenting on the exhibition in Cardiff, said: "Wales is such a place that is steeped in history and cultures, and the rich historical and cultural deposits embedded with her are exactly why we choose National Museum Wales, Cardiff to host the first appearance of Dazu Rock Carvings Art outside of China.

"As a world cultural heritage, Dazu Rock Carvings should not only be taken as a treasure for local people of Dazu, but should also be recognized as a cultural property of the whole world, and both the artistic and historical value should be shared and appreciated by world people".

The museum has made a film about the exhibition that you can watch on YouTube.

You can also keep up to date with Dazu on Facebook and follow the National Museum Wales on Twitter.

Aerial view of Goldcliff Point © Royal Commission on the Ancient and Historical monuments of Wales

The series follows researchers from the Royal Commission on the Ancient and Historical Monuments of Wales who are joined by a new presenting team - Wales and the History of the World presenter Eddie Butler, and Heledd Fychan.

In tonight's programme Commission reserachers visit three locations in Wales. Goldcliff Church in Monmouthshire, Wig-wen-fach, a derelict cottage in Cardiganshire, and the Llantisilio Chain bridge.

Wig-wen-fach cottage in Cardiganshire © Royal Commission on the Ancient and Historical monuments of Wales

The Royal Commission on the Ancient and Historical Monuments of Wales have created excellent, in-depth guides to each subject featured in tonight's programme. Read the guides on their website and view images relating to Hidden Histories on their Flickr photostream.

Hidden Histories begins tonight, Thursday 20 January, at 7.30pm on BBC Two Wales.

Llanelly House is a Grade I listed house in the centre of Llanelli in west Wales.

The house is the former home of the Stepney family. Built in 1714 by Thomas Stepney, MP for Carmarthenshire, the house was constructed on the site of their previous family home, and at the time was an example of super-fashionable architectural design: a Roman-style dwelling. The obvious grandeur of the house - inside and out - was a nod to the immense wealth and power of the Stepneys.

The Llanelli Historical Society and Llanelli History both have comprehensive histories of the house on their websites.

Until recently most of the work in securing a future for the building has taken place outside of the public gaze. Emergency strengthening work inside the house has ensured the immediate structural survival of the building and in June 2008 the Trustees of the Heritage Lottery Fund approved the joint funding application submitted by the Town Council and the Carmarthenshire Heritage Regeneration Trust, with a grant £3.4 million plus £146,500 towards project development costs.

This year, Llanelly House has been part of the Open Doors initiative, the largest annual free celebration of architecture and heritage to be held in Wales.

Throughout September the house is running a number of escorted tours, and Wales History was lucky enough to have been invited to join a tour of this beguiling building.

Estelle Evans and Lisa Bancroft begin the tour by explaining how much of the original house has been lost.

The house has now been stripped right back to its skeletal state. Each new timber beam or joist revealed by archaeologists is painstakingly recorded and logged with numerous partners including CADW, English Heritage and the National Museum of Wales.

Upstairs in Llanelly House

Clumsy plyboard panelling and make-do repairs have skilfully been removed and delicate pictures have been sent to the National Museum of Wales for restoration.

The roof of Llanelly House

For the majority of the time that Llanelly House has existed, it has been more widely used as a home to the working class of Llanelli than it has been to the gentry.

The remaining building, which is only a part of the original house, been sliced and split into tenements, used as a telegram office, a shop and council buildings.

Each successive generation has left their mark on Llanelly House. On a daily basis, the house reveals a new secret or evidence of past lives.

The room on the right is said to be haunted by the ghost of servant Mira Turner

The restored Llanelly House will have a much wider purpose than to provide a snapshot of the elegant splendour of a Georgian House. At the very core of the development plans are community initiatives and schemes which aim to ensure it is history of the people of Llanelli, and their stories, that are central to the house.

Estelle Evans, the Community Development Officer of Carmarthenshire Heritage Regeneration Trust (CHRT) has been working closely with local schools and other community groups on a wide number of initiatives. One project is called Move In Here.

"We want to know why people have come to Llanelli," she says. "Why did they move to the area, be it only a few miles into the town centre? Why did they stay and why did they move away? There is always a reason behind that. We can analyse that information."

By 1873 the Post and Telegraph Offices were located in Thomas Stepney's old study in Llanelly House. This is the Post Office safe.

Stepneys' grand panelled office on the ground floor had functioned as a Post Office up to 1896. Two weeks ago an unremarkable panel was pulled back to reveal shelves groaning under a bounty of official paperwork. This is where people from around Llanelli and the surrounding area would come to get their emigration papers for America. It was also the first point of call for people coming to work in Llanelli from other countries.

Lisa Bancroft, Development Manager for CHRT is tasked with ensuring that Llanelly House balances the demands of restoration and long-term sustainability. She explains:

"The house itself when you walk in will ostensibly be renovated and restored to its pristine condition of the 18th century. It will be very beautiful. It is a very good look, it is very modern, very light but it has to pay its way.

"Downstairs the house will be very much for people to use, to chill out in with a restaurant, shop, workspace area and events. Then upstairs we will be interpreting the house in different ways, using different characters".

To read more about the developments at Llanelly House visit their website.

Open Doors is organised by the Civic Trust for Wales on behalf of Cadw, the Welsh Assembly Government's historic environment service. Find out more the initiative and places to visit on the Civic Trust for Wales website.