Issue no 56, December 2000

Chris Tolan-Smith recalls the brick pit where artefacts were first recognised as signs of humanity's great antiquity

Many of archaeology's greatest advances have been made as the result of systematic research by specialists over decades. Many others were made through serendipitous chance. Never, perhaps, was this more true than at Hoxne in Suffolk, where the great antiquity of humanity was first recognised in a brick-pit in the closing years of the 18th century.

In the summer of 1797 - the exact date is not known - John Frere, a gentleman farmer and graduate of Cambridge University, was journeying from his home at Roydon Hall near Diss in Norfolk to Eye in Suffolk. His route took him through the small Suffolk village of Hoxne (pronounced `Hoxen') on the banks of the Dove, upstream of its confluence with the Waveney.

A man with wide interests in the natural sciences and antiquities, Frere paused to watch workmen digging clay for bricks in a pit just south of the village. He was particularly struck by the material he saw them using to fill in potholes and ruts in the adjacent road - regularly shaped, triangular flints which Frere immediately recognised as human tools of the kind now called handaxes. The significance of his perception was momentous. Previously handaxes had been typically regarded as mythical or magical objects, `elf shot', thunderbolts and the like.

Frere inquired where they had came from and was shown a layer of gravel about 12 feet below the surface, underneath layers of sand and brick-earth. He interpreted the overlying deposits - correctly - as riverine. However, he noted that the site lay near the top of a hill. These two observations led him to infer that the handaxes must be of great antiquity. They were `weapons of war', he concluded, `fabricated and used by a people who had not the use of metals . . . (which) may tempt us to refer them to a very remote period indeed; even beyond that of the present world.'

Frere communicated his discoveries and observations in a letter to the Rev John Brand, then Secretary of the Society of Antiquaries. The letter was read on 22 June 1797 but received little comment other than the Secretary's thanks for his `curious and most interesting communication.' It was published in Archaeologia in 1800, but at this time most authorities still adhered to the literal truth of the Bible and placed the date of Creation at 4004 BC. Over half a century was to elapse before the significance of Frere's discovery was recognised.

During the first half of the 19th century scientists of various disciplines - geologists, biologists, palaeontologists, antiquaries - inched towards an acceptance of humanity's great antiquity. From around 1810 flint tools began to be excavated in large numbers from the caves and rock shelters of the Périgord. In 1828, more were found associated with extinct animal bones in Kent's Cavern near Torquay in Devon. Similar discoveries were made across Europe. Meanwhile, Charles Darwin was working on his Origin of Species which was published in 1859.

In that same year, the archaeologist John Evans and geologist Joseph Prestwich visited Abbeville in northern France. There, the French customs official Jacques Boucher de Perthes claimed to have found handaxes and other tools associated with mammoth bones in undisturbed deposits some 11 feet below the ground surface. His British visitors were impressed. Academic attention then swung back to Hoxne. In a paper read to the Royal Society on 26 May 1859, Prestwich described a visit made to the brick-pit, a small excavation to test Frere's findings, and the inspection of artefacts and animal bones found at the site. With Evans, he confirmed Frere's observations. From that date onwards the Hoxne brick-pit has remained one of the most important sites in British Palaeolithic archaeology.

Systematic excavations by the British Association in 1896, and later by Ipswich Museum and Cambridge University, established the climatic context. A major interglacial period - the Hoxnian - was identified between the Anglian and Wolstonian glaciations. This stage is now dated to roughly 425-375,000 years ago.

The main archaeological excavations at Hoxne were undertaken by a team from Chicago University during the 1970s led by Ronald Singer. This work established that the early humans who visited Hoxne - probably archaic Homo sapiens, although no human remains were found to prove it - probably did so about 320,000 years ago during a relatively temperate stage of the Wolstonian glaciation. Ironically the finds that made Hoxne famous date to a different period from the one to which Hoxne has given its name.

The evidence from the Chicago excavations suggests that the site witnessed two or three periods of occupation during which groups made brief halts beside a lake or slowly moving body of water. They made handaxes and other flint implements and used them to butcher the carcasses of horses or red deer they had either scavenged or hunted.

Hoxne also showed that technological change in the Palaeolithic did not follow a simple trajectory of progress, as had previously been believed, from simpler to more sophisticated forms of tool. Instead, finely made ovate handaxes were found to predate more crudely made triangular handaxes. This need not be seen as an example of technological decline but may reflect the presence at the site of social groups with different technological traditions.

Groupings of stones at Hoxne were interpreted as `structures' - the earliest yet found in Britain. Their function was unclear, but they may have been platforms used to consolidate the muddy, trampled ground surface by the shore of the lake.

The Hoxne brick-pit - overgrown and long since worked-out - can still be seen on the east side of the road to Eye. Frere himself died in 1807, 52 years before Prestwich and Evans established the authenticity of his discoveries. However a memorial plaque has recently been erected in Finningham Church, near Hoxne, which pays long overdue tribute to his pioneering observations, which made such an important contribution to the fundamental reappraisal of what it means to be human.

Chris Tolan-Smith is a Senior Lecturer at Newcastle University

Metal came relatively late to Britain. But it was here that a remarkable new compound was perfected. It was called bronze. Paul Budd reports.

Four thousand years ago, on the gentle slope of a south Wales hillside, a small hole was dug and a precious cargo consigned to the earth. The buried items would have been recognisable to the builders of the medieval castle that came to share the hillside three millennia later. Familiar too to the Victorian nobles who rebuilt those fortifications a thousand years after that, creating a splendid fairytale folly at Castell Coch in the South Glamorgan countryside.

Indeed, the contents of the ancient pit were clear enough to the metal detector user who brought them back to the light of day in 1984.

The buried treasure, known as the Castell Coch hoard, consisted of three weapons, a dagger and two halberds (dagger-like blades hafted as axes), made and deposited in about 2200-1800 BC, not long after the beginning of metal making and use in Britain.

But who made them and where? How did the technology of mining, smelting and weapon making come to these islands in the first place? Today it is not just the form and context of finds like those at Castell Coch that help us to answer these questions, but the very metal itself. The latest archaeological research shows that, although metallurgy came relatively late to Britain, its arrival here sparked a technological revolution whose consequences reached every corner of Europe. It was in Britain that metal workers perfected a new metal. It was called bronze.

For more than half a century archaeologists have grappled with the enigma of Britain's first use of metals. It appears to have taken the art of metallurgy more than 2,000 years to travel from the ancient Near East and Balkans to Britain, and its dramatic arrival in about 2500 BC prompted early scholars to suggest direct contact between Britain and the great metal-using civilisations of the Mediterranean. The images evoked were of roaming metal prospectors searching savage lands for raw materials. The reality may be more prosaic, but is no less interesting.

In fact, the long history of metallurgy was not just a Mediterranean affair. For its origins we have to look several thousand years before the Castell Coch artefacts were deposited in their shallow sanctuary. The very earliest copper objects come from settlements and graves of the late 8th/early 7th millennium BC in Mesopotamia and Anatolia, and these are thought to be the products of rare outcrops of copper metal (not copper ore) found in some parts of this copper-rich area.

The momentous discovery of smelting came later, in the mid-5th millennium, seemingly independently in Anatolia, Mesopotamia and the Balkans. By this time copper miners were hard at work at places such as Aibunar in Bulgaria and Rudna Glava in Serbia, where rich veins of copper oxide and carbonate minerals were being emptied to make what must have seemed an entirely new kind of material. Hard enough to sharpen to a cutting edge, yet tough enough not to shatter. Infinitely remeltable and reuseable.

This wonder material, copper, could be smelted with relative ease from the weathered and oxidised Balkan ores, simply by heating them in a bed of charcoal. With a little assistance from bellows, this pure carbon fuel could produce a high temperature and maintain the chemically reducing conditions needed to convert the ore to metal. Output was impressive and the Balkan miners were soon possessed of large numbers of massive copper axe-hammers, adzes and chisels. Their success however was not to continue without break.

After perhaps a thousand years of Balkan copper production, the deposition of copper in hoards and graves faded away. The technology was not lost though. As dramatically as it appeared to decline, metallurgy was back, but this time in a different location and with a new sort of metal. In the mid-4th millennium, arsenical copper was now taking centre stage with a new focus on Alpine and sub-Alpine Europe. A similar copper-arsenic alloy was developed in the old copper-producing centres of the Near East, although there the transition took place without the production hiatus apparently experienced in Europe.

Exploitation of the rich Alpine copper required the development of a new technology. Unlike the Balkan ores, the Alpine deposits were mostly of copper sulphide minerals. Unusable as mined, these had to be roasted before smelting to convert the sulphide minerals to the oxides that would have been familiar to the Balkan smelters. In practice, lumps of sulphide ore were placed on a hot wood fire and stirred round, to introduce plenty of oxygen and convert the ore to copper oxide. The oxide ore was then smelted in an enclosed furnace heated by charcoal with as little oxygen as possible to reduce the ore to metal. Such roasting beds and smelting furnaces dating from the later Bronze Age have been found in the Mitterberg region south of Salzburg.

The new focus on arsenic-rich Alpine ores and the widespread occurrence of arsenical copper artefacts in the 4th millennium is something of a `chicken and egg' conundrum for modern scholars. Did metal-workers deliberately seek out deposits rich in arsenic (a metalloid element) or was the arsenic an unintended inclusion?

Recent research suggests that early metal workers knew exactly what they were doing in using these ores. A significant addition of arsenic to copper produces better mechanical properties, and higher levels produce a metal of striking silvery appearance. Artefacts with higher levels tended to be `high status' objects such as knives and daggers, while everyday tools, such as the 4th millennium BC Iceman's axe, contained less. The proportion of arsenic in artefacts ranges from less than 1 to 7 per cent - never more than that - while ores can contain up to 30 per cent, suggesting that arsenic quantities were being controlled.

Such control may have been exercised by mixing arsenic-rich copper with other types of copper, both in pure form and as recycled tools.

The evidence for such mixing comes from slightly later periods, but might apply equally to the 4th millennium. At the mine site at Ross Island in Ireland, for example, dating from the mid-3rd millennium, the ores are varied, containing anything from a few to about 30 per cent arsenic. However, the metal produced was much more consistent, suggesting that the ores were mixed. Later still, in the 2nd millennium, the Great Orme mines in North Wales produced perhaps hundreds of tonnes of copper at a time when most artefacts contained some degree of arsenic, and yet the Great Orme ores contained no arsenic whatsoever. The Great Orme metal was clearly not used without some degree of adaptation.

Whatever the truth of central Europe's arsenical copper in the 4th millennium, Britain remained literally in the Stone Age. It would be a thousand years before the island periphery of north-western Europe was to experience metallurgy at all. And yet when it came, the metals revolution took off with explosive technological pace. Within a few hundred years not only was a Continental-style arsenical copper industry thriving here, but by about 2000 BC the harder, tougher alloy of copper and tin known as bronze had also been invented. It replaced arsenical copper across Europe and dominated the European metals scene until the coming of iron more than 1,000 years later.

It is perhaps not strictly true to say that bronze was invented in Britain. The very earliest combination of tin and copper is found in Anatolia, but Near Eastern bronze contained less tin, in less standardised quantities, than was found in British bronze. Put simply, it was inferior bronze. In Britain, bronze was produced from the outset with an almost standard composition of 8 to 12 per cent tin, ensuring the optimum mix of qualities. For archaeologists the rapid establishment and spectacular success of metallurgy in the British Early Bronze Age, from 2500-2000 BC, is something of a quandary. How did metallurgy arrive in an apparently advanced state? Who brought it and why did it take off here so well?

If Aegean prospectors could be ruled out as the fathers of British metal making - and there is simply no evidence in Britain of contact with Aegean civilisations - could metal tools and weapons have filtered across the Channel, followed perhaps by those skilled in their manufacture? If this latter scenario were true, we might expect to see a cluster of early metal finds in south-eastern England, but we do not.

In fact, the region where early tools and weapons suddenly appear in large numbers is south-west Ireland, predominantly in the form of simple `flat' axes. Wherever it was made and traded, more of it was left behind in the rugged Atlantic coastal landscape of Munster than anywhere else. This Irish metal was not inferior stuff either. What was being made and deposited was not the simple copper of the earliest European metallurgy, but arsenical copper, the superior material pioneered in Alpine Europe and, by this time, also commonplace throughout the Mediterranean as far west as Spain and Portugal.

So how did this advanced technology suddenly come to Ireland, and why? Who were these metal makers? To a previous generation of archaeologists such developments could only be explained by the invasion and settlement of new, technologically advanced, people. If not Greeks prospecting for precious ores, perhaps Iberian settlers made their way north along the Atlantic coast seeking out sources of the arsenic-bearing copper ores with which they were familiar.

This notion of a mass movement of people, even an invasion, found support elsewhere in the archaeological record. The arrival of metallurgy was not the only big change taking place in the middle of the 3rd millennium, but the period also saw the appearance of beaker pottery in the British Isles. These highly distinctive vessels, often buried with the dead, were widespread in central Europe and Iberia before they were used in Ireland. Was there a link?

Today, there is some reluctance to see the arrival of a new pottery form, however distinctive and ubiquitous, as necessarily a sign of the arrival of a new population of immigrants. New artefacts and burial practices can, after all, simply reflect changing ideas or trade, which was well-established along the Atlantic seabord in this period. But the idea of a Beaker Culture, with its distinctive pottery, funerary practices, flint arrows and established tradition of metal making, is hard to cast off.

Not many years ago, this would have been about as close as it was possible to get to meeting the metal makers who brought metallurgy to the British Isles and launched the Age of Bronze. But now our understanding is being transformed by a combination of archaeological research on the ground and scientific investigation in the laboratory. When the notion of the Beaker inspired birth of Irish metallurgy was first aired, there was no evidence for prehistoric mining in that country. Proponents of the theory pointed to geological data for the occurrence of `fahlerz' ores in the region, linked, they said, to the distinctive arsenic-rich Munster axes. However, when prehistoric mines were identified in the 1960s at Mount Gabriel on the Mizen Peninsular on the far south-west of Co Cork, they were a miserable affair indeed - shallow scrapings on the hillside devoted to the recovery of ore which was almost devoid of copper and without arsenic. It seemed an unlikely base for production on the scale suggested by multitudes of axes.

The breakthrough came in the 1990s with the excavation of the earliest prehistoric copper mine yet discovered in the British Isles. At Ross Island, on the eastern edge of Lough Leane in Co Kerry, the archaeologists struck lucky. The site had been worked for copper in the early 19th century and the miners had found older workings. Systematic excavation and radiocarbon dating now show that the earliest of these date to the mid-3rd millennium.

Moreover, Ross Island is unique in preserving not just the mine itself, but also the miners' work camp in an area of huts and ore processing installations immediately adjacent to the workings. Among the shelters, animal bone food waste and worked flint, were numerous early Beaker sherds confirming the long-suspected link between the users of the distinctive pottery and the mining of metal. Equally striking was the ore itself, not the low-grade copper of Mount Gabriel, but rich arsenic-bearing sulphide ores of the fahlerz type. From a single site all the theories could be confirmed.

Although they do not turn up in the numbers found in Munster, early flat axes have been recovered from all over England, Wales and Scotland. These axes have been chemically analysed and share the distinctive arsenic, antimony and silver impurity pattern of the Munster finds. It seems reasonable to conclude that these earliest British metal artefacts were indeed imports, not from the Continent but from the mines of Munster - of which Ross Island was probably only one of several.

But this Irish dominance was not to last. By the time the Castell Coch weapons were made, axes, daggers and halberds were not just being made in Ireland, but also in the metal-bearing regions of Wales, Scotland and England. Within a few hundred years of the first roasting of Ross Island's ores, copper mines were opening up at places like the Great Orme and Parys Mountain in North Wales, Cwmystwyth in central Wales and Alderley Edge in Cheshire. The relatively pure copper of the British mines was fed into the pool of arsenic-rich copper in circulation to produce ever-increasing numbers of metal tools and weapons.

But what of the development of bronze? Some of the copper alloy tools made around 2000 BC, including two of the Castell Coch finds, contained significant traces of nickel. We have now tracked down the source of this distinctive ore, and it provides us with the missing link between copper alloys and the development of the new metal made with tin. Different ore sources have distinctive lead isotope ratios which can be used to provenance archaeological artefacts, and the Castell Coch artefacts were highly unusual in having very high lead isotope ratios of a sort that can only occur when uranium is present within the ore. Further analysis of the ratios provided the geological age of the deposit which allowed us to pinpoint the source of the ore even more accurately. Taken together, the data showed that these particular artefacts were made from copper ore that could only have come from one place in north-western Europe - Cornwall.

The Cornish provenance of the Castell Coch hoard and other non-Irish tools and weapons leads us directly to the pioneers of bronze, because it confirms that a mining tradition was established in Cornwall at the time of the invention of bronze, in an area that contains one of the richest tin fields in the world. Along with Afghanistan, Cornwall is one of only two possible major sources of the tin used in bronze throughout Europe after about 2000 BC. No prehistoric mines have yet been found in Cornwall but this is hardly surprising: the landscape has been eaten away by coastal erosion and turned upside down by the vast scale of the post-medieval tin industry. All prehistoric evidence may have been destroyed.

It is unlikely that bronze tools were actually made in Cornwall. Metallurgy probably took place nearer the copper mines of Great Orme and elsewhere, with smelted tin or (more likely) tin ore traded up from Cornwall to be mixed in with molten copper. Strangely enough, as the source of one of Europe's most valuable commodities, Cornwall contains few signs of conspicuous wealth in the Bronze Age period. There are few great monuments or burials.

This has led some archaeologists to speculate that it was not locals but middlemen who made most of the profit out of this exceptionally lucrative international trade in tin. And who were the middlemen? The most impressive signs of wealth in the Bronze Age are found in the barrows and monuments of Wessex. Were the Wessex chieftains the `barrow boys' of the Bronze Age economy? It is an intriguing thought, and it may just be true.

Paul Budd is an Honorary Research Fellow at the University of Durham and a specialist in archaeometallurgy

Offa's Dyke used to be thought of as just a boundary line. We now think it was built in earnest for defence against the mighty kingdom of Powys. David Hill explains

Conflict between the medieval English and Welsh kingdoms was traditionally seen as an uneven match: English aggressors versus Welsh victims. Historians have held this view not only of the 13th century wars of conquest, but of encounters in the Anglo-Saxon period too.

And what better symbol of Anglo-Saxon high-handedness than Offa's Dyke, that great earthwork along the Welsh border? For years, this has been regarded as a frontier, a symbolic boundary line that proclaimed: Welsh, stand back. Beyond this line is English land.

Offa, builder of the Dyke and king of Mercia (the kingdom of middle England) from 757 to 796, could have been just the man to take such a line.

One of the great figures of his age, he stood nearly on a level with Charlemagne, and dealt directly with the Pope over the reorganisation of Mercian dioceses. He presided over a period of growing trade and urbanisation. To such a man, who were the Welsh?

And yet, it was not so. My own research tells a different story. Far from being supine victims, the Welsh - over the Dyke in Powys - were a major force. Rather than a symbolic boundary, the Dyke was a defensive barrier. Powys was on the warpath against the English, and often won. The Dyke was nothing less than Offa's Western Front.

The traditional view stems directly from Sir Cyril Fox's fieldwork in the 1930s. His book Offa's Dyke had enormous influence and is still used as a textbook in many universities. Fox could not believe that the Dyke was a defensive barrier. Firstly, he thought it had been built `from sea to sea' - from the NorthWales coast to the South Wales coast - following a remark to that effect made by Asser, the 10th century biographer of King Alfred. But along this entire extent there were many `gaps', Fox saw, undermining the Dyke's defensive usefulness.

Also, Fox was a product of his era. He wrote at a time when the British Empire was at its greatest extent, and it was natural for him to think in terms of boundaries, set after a phase of imperial advance. Defensive lines he equated with the trenches of the First World War, in which thousands of men stood shoulder to shoulder for months or years on end, rightly pointing out that Mercia would have been unequal to such a commitment.

But Fox missed the point - or several points. Permanent garrisons are not the only way of defending an extended bulwark. The Dyke need not have originally run from sea to sea. The famous `gaps' in the Dyke are a red herring.

Dyke's limits

Let us start from what we know. The major section of what is today called Offa's Dyke runs for 64 miles from Rushock Hill near Kington in Herefordshire to Llanfynydd near Wrexham. Between these points it survives as a continuous earthwork except for a length along the River Severn in Montgomeryshire.

To north and south of this section are gaps, followed by short intermittent sections of earthwork now called `Offa's Dyke' - but which are no such thing. Fieldwork proves it.

The section to the north, a few miles south of Prestatyn, was never connected to Offa's Dyke (I have excavated both ends, and it stops). It is also of completely different construction - parallel ditches with a bank between, as opposed to the bank and deep ditch to the Welsh side seen on Offa's Dyke. This earthwork is complete in itself and was, I believe, a late Norman boundary.

To the south, intermittent short lengths of earthwork cross the Herefordshire Plain to reach the River Wye, but extensive geophysical survey and excavation have failed to provide even a hint that this was once a continuation of Offa's Dyke. The Dyke's ditches were 18 feet wide and 6 feet deep. If they were there, an archaeologist couldn't miss them. But they are not.

Continuing south, there follows a 37 mile gap from the Wye to Redbrook in Gloucestershire, where a further 10-mile stretch of earthwork begins, again now called `Offa's Dyke'. This is similar in construction to the main Offa's Dyke, but it faces south rather than west. Considering the gap of 50-odd miles between it and the main Dyke at Rushock Hill, there is no reason to believe it was once part of the same earthwork.

It is only Asser's phrase, that Offa built his Dyke de mari usque mare, `from sea to sea', that inspired all this fruitless hunting about for missing sections. The phrase `from sea to sea' was a literary conceit, a cliché, often used to describe earthworks even when they began and ended on dry land. An example of this is the great 8th century Danish earthwork across Jutland, the Danewirke, described as running from sea to sea in the Annales Regni Francorum, but which in fact extends for only 14 miles from Hedeby to Hollingstedt, some 10 per cent of the width of Jutland. It was linked to the coasts by inland waterways.

A rational view would be that the main continuous section of Dyke along the central Welsh border is a complete earthwork in itself. So why just build this 64 mile stretch?

The precise boundaries of the early Welsh kingdoms are uncertain, but it is highly plausible that this section of Offa's Dyke marks the border between 8th century Mercia and Powys. To the north was the frontier between Mercia and Gwynedd, and to the south between Mercia and Ercing and Gwent. There is evidence that Mercia was at war with Powys, but not with the other states to north and south. A defensive boundary was therefore needed only in the middle.

Powys wins

The main evidence comes from a text carved onto a free-standing cross shaft known as the Pillar of Eliseg (from the name of the king it commemorates), which stands a few miles west of the northern end of the Dyke near Llangollen, just north of the Abbey of Valle Crucis in Powys. It was a famous landmark which gave its name to the valley and later to the abbey nearby.

The cross was thrown down and broken in the Civil War, and its inscription is now partly worn away. The surviving portion reads:

Concenn, son of Catell, Catell
son of Brohcmail, Brohcmail son
of Eliseg, Eliseg son of Guoillauc,

Concenn therefore being great
-grandson of Elise erected this stone to
his great-grandfather Eliseg.

It was Eliseg who annexed
the inheritance of Powys ...
throughout nine (years?) from the
power of the English
which he made into a sword-land by fire

Whosoever shall read this hand-inscribed
stone, let him give a blessing on
the soul of Eliseg.

Concenn died in 854. He and Eliseg were kings of Powys, and Eliseg is usually dated to the mid-8th century, making him Offa's contemporary. In commemorating nine years of successful Welsh struggle against the Mercians, the pillar not only records the 8th century successes of the house of Powys, but also reflects the attitudes of its rulers in the 9th.

Where this land, `the inheritance of Powys', lay is not clear. An area close by, such as the Vale of Llangollen, is a possibility. My feeling is that the land (wherever it was) was not recovered by Mercia, and that the Dyke was built after Eliseg's campaign representing a fall-back position.

What is clear, above all, is that Offa was confronted with a serious military threat on his western border. An obscure battle between Powys and Mercia, recorded for the year 760 in the Annales Cambriae, may have been part of the same campaign.

Mercian guards

As a defensive barrier, how did the Dyke work? It was certainly nothing like Hadrian's Wall, with permanent garrisons stationed in forts and milecastles. However, using mobile patrols and well-placed signal beacons, it would have been possible for the Mercians to police the Dyke with relatively few men.

The topography of Wat's Dyke, another Mercian earthwork to the north, is instructive. Wat's Dyke runs for 40 miles - as I have shown through extensive fieldwork - along the edge of the Cheshire Plain from Maesbury hillfort on the River Vrynwy to Basingwerk hillfort by the sea. It is very similar to Offa's Dyke, but better made. It is undated, except for a single radiocarbon date from a fire underneath the Dyke which indicates it must be later than the 6th century. Its positioning suggests to me that it was built in the 850s, as the land to the west of it - Gwynedd and North Powys - briefly became a unified state at this time.

To send a signal the whole length of Wat's Dyke, you need only three major beacons - near Chester, at Snow Hill south of Flint, and on the Breidden. Moreover the Dyke links nine hillforts, with Old Oswestry at the centre, and they may have served as camps for the patrols. Offa's Dyke needs perhaps six or eight major beacons, each of them positioned one or two miles back in Mercian territory.

Although we know that the Anglo-Saxon beacon system was highly developed, beacon sites - large thatched bonfires which were rarely lit - are hard to find archaeologically. We may have found one intermediate beacon site on Wat's Dyke but we cannot be sure. There was no burning.

Patrol camps on or near Offa's Dyke are equally elusive. The hillfort of Sutton Walls near Hereford is a possible site but its ditches were filled with toxic waste in the 1960s so any evidence is lost. Indeed the remarkable lack of Anglo-Saxon evidence from either Offa's or Wat's Dyke suggests that people were not settling, or even spending much time in these wild border zones.

The profile of Offa's Dyke is unmistakably defensive. It consists of a deep U-shaped or V-shaped ditch on the Welsh side, with a steep-faced turf bank with a flat top and gently-sloping rear.

There is also some evidence that it was crowned with some further defensive structure. At Llanfynydd, at the north end of the Dyke, we found stone blocks in the primary fill of the ditch, suggesting a collapsed wall. Elsewhere we conjecture a palisade, but vegetation has disturbed the evidence. Timbers surviving at the Danewirke in Jutland shows that it, at least, carried a palisade.

We cannot know how successful the Dyke proved in resisting further Welsh attack. Its rough coincidence today with the English-Welsh border suggests it may have demonstrated its worth. In the end, Mercia's demise came from elsewhere. A century after Offa's death, Mercia had been subsumed within a larger England dominated by the former kings of Wessex.

England under Offa

The 12th century chronicle of Simeon of Durham contains a unique reference to what seem to be towns in England in the 8th century. Under the year 764, he states that a number of places were devastated by fire: `The calamity struck Stretburg [Cirencester?], Winchester, Southampton, the city of London, the city of York, Doncaster and many other places.'

The implication is of places so densely packed that fire could sweep through them. For years the reference intrigued historians, because it was thought that the sophisticated, urban Anglo-Saxon economy began only with Alfred the Great in the later 9th century.

Towns were certainly extended and revitalised in Alfred's period. However, dramatic archaeological discoveries over recent decades have shown that towns and international trade had their origins in England more than 100 years earlier - during, or even before, the reign of King Offa of Mercia. Many of the sites for which we have evidence match those in Simeon's list.

We now know that Southampton (which I excavated with Peter Addyman from the late 1960s), Ipswich and London were all important trading centres, or wics, from the early 700s. All lay within Mercia, whose power in the 8th century covered the whole of England south of the Humber. Excavation has shown that defended settlements or proto-towns developed also at Hereford, Worcester, Gloucester, Tamworth, Winchcombe and elsewhere within the Mercian heartlands.

One of Offa's best-known achievements was his reform of the coinage - replacing barbarous sceattas with beautiful gold and silver coins, the first pennies - and it is likely that Mercia's towns were the focus of a new international market economy. The weight and fineness of Mercian coins remained in step with Continental coins during the 8th century, clearly demonstrating a trading link. Certain goods, such as millstones made of volcanic lava, have been found traded across Europe from Tamworth to Poland.

Perhaps the most curious piece of evidence for the extent of Mercian trading influence is an 8th century gold imitation dinar - an Arabic coin - found in central Italy. On one side is the legend `Offa King of Mercia', and on the other `There is no God but God and Allah his Prophet'. It must reflect trade, but the circumstances in which such a coin was made remain a fascinating mystery.

David Hill is Senior Research Fellow in the Centre for Anglo-Saxon Studies, University of Manchester