A basic henge is simply a, roughly, circular space, enclosed by a ditch and bank earthwork, with an entrance, or entrances, leading to the centre. As a rule (there are, of course, exceptions), the bank is built up on the outside of the ditch – an arrangement usually regarded as being unsuitable for defensive purposes. Most henges contained various types of feature – for instance, arrangements of stones, timbers or pits. It is generally thought that they were ceremonial centres, where people would gather together to take part in religious rituals and other communal activities. Stone circles (where a space is enclosed by standing stones), presumably fulfilling a similar role, were also constructed. Some henges combine a ditch and bank with a stone circle – including the two most famous (and magnificent), Stonehenge and Avebury, both in Wiltshire.

The archaeological term ‘henge’ is actually a back-formation from the name Stonehenge (coined in Anglo-Saxon times – meaning ‘the hanging stones’), but Stonehenge, which represents the culmination of stone circle engineering, is not at all a typical henge.

STONEHENGE

Stonehenge's first chronicler, Henry of Huntingdon, mused on ‘the how’ and ‘the why’ of its construction, and, nine centuries later, archaeologists are still trying to provide satisfactory answers to those two basic questions. Considerable progress has, however, been made in unravelling Stonehenge's history, and, thanks to Radiocarbon Dating, answering a third important question: ‘the when’.

In its first form, begun about 3000BC, Stonehenge comprised a ditch and bank earthwork, enclosing a area some 91.7 metres in diameter, and, it now seems possible (perhaps likely), a circle of standing stones. Uncharacteristically for a henge, the bank was on the inside of the ditch. (There was also a low outer bank, now severely eroded by agriculture.) When new, the chalk bedrock of Salisbury Plain would have ensured the earthwork stood out boldly in the landscape. There were two entrance causeways – the main, larger, one to the north-east and a smaller one to the south. Running just inside of the earthwork circle is a circuit of fifty-six pits called Aubrey Holes. Most of the thirty-four that have been examined contained cremation burials. In recent years, the most popular theory has been that the Aubrey Holes originally held timber posts, but archaeologists of the Stonehenge Riverside Project (SRP) re-opened one in August 2008, and the condition of its chalk base led them to believe that it once supported a standing stone. Researching archive material revealed that similar crushing of the chalk had been observed, in other Aubrey Holes, during previous excavations. The SRP have proposed that the Aubrey Holes originally supported ‘bluestones’, which have generally been seen as much later arrivals at Stonehenge. (The bluestones are a heterogeneous selection of stones, apparently originating in the Preseli Hills of south-west Wales, some 150, as the crow flies, miles distant.)

Not long after Stonehenge's inception (from c.2900BC), there appears to have been a change of heart. There was some backfilling of the ditch. The henge seems to have become neglected. Silt accumulated in the ditch. Plant life flourished. The, once crisp, contours of the earthwork became softened by erosion and vegetation. On the other hand, there is a complex of post-holes – the remnants of timber structures – within the henge, between the centre and the southern entrance, and at the main entrance, which could date from this time. At any rate, in about 2600BC Stonehenge entered its final period of development, in which stones were arranged and rearranged in the centre of the henge, eventually producing the monument whose impressive wreckage remains today.

The first appearance of bluestones in the middle of the henge – indeed, their first definite appearance anywhere on site – was in a concentric double arc setting. The evidence for this placement is provided by the, so-called, Q and R Holes. There are no reliable radiocarbon dates for the double arc, but Richard Atkinson's excavations, in the mid-1950s, indicated that it was the earliest stone setting in the henge's centre. As a result, it has usually been placed round about 2600BC – just a short while before the arrival on the scene of the massive ‘sarsen’ stones in about 2500BC – the theory being that this rather modest bluestone arrangement was quickly abandoned and removed, to make way for a much more ambitious scheme. The SRP has, however, questioned the supposed stratigraphic relationship between the bluestone arcs and the sarsens, and suggests that the settings were contemporaries – that they were built as a single monument.

Sarsens are naturally occurring sandstone slabs, and, it is generally believed, they were sourced from the Marlborough Downs, almost 20 miles to the north. A circle (30 metres in diameter) of thirty sarsen uprights (standing approximately 4 metres above ground level), topped off by a continuous circuit of sarsen lintels, was erected around a horseshoe arrangement (the open end pointing in a north-easterly direction) of five, massive, sarsen ‘trilithons’. Construction of this megalithic masterpiece would have taken an enormous number of man-hours. Once the, not inconsiderable, task of dragging the rough sarsens to the site had been accomplished, these, extremely hard, rocks were shaped and smoothed, and had joints sculpted into them, using the most rudimentary of stone tools. Having levered the uprights vertical, the lintels (6 tons plus) then had to be raised (up to 7 metres above the ground), and dropped into position. (The Q and R Holes lie between the sarsen circle and the trilithon horseshoe.)

As already mentioned, in what has been the generally accepted interpretation, it is suggested that the bluestones – much smaller than the sarsens: around 2 metres long, 4 tons in weight – arrived at Stonehenge c.2600BC. The SRP has now proposed that there were bluestones planted in the Aubrey Holes some four centuries before that. Further, in 2009 the SRP excavated a newly discovered feature, just over a mile to the south-east of Stonehenge, adjacent to the River Avon. It had been the site of a small stone circle – about 10 metres in diameter, with an estimated twenty-five standing stones – at the same time as Stonehenge's beginnings. The SRP have proposed that these stones were also bluestones. They suggest that the stones from both the Aubrey Holes and this newly found monument (which has been dubbed Bluestonehenge) were recycled in the centre of Stonehenge.

Professors Timothy Darvill and Geoffrey Wainwright consider the bluestones to be Stonehenge's raison d'être. They believe that they were thought to have healing properties, and that Stonehenge was “a prehistoric Lourdes” – a place of pilgrimage, to where people would travel in the hope of being cured. The professors also believe they have found the exact place in the Preseli Hills from where the stones were collected. Geological evidence, however, tends to suggest that the stones are from a much more generalised area. There were about eighty bluestones at Stonehenge. To shift that number of, 4 ton, stone slabs that far, over land and water, would have been an incredible undertaking, indeed, too incredible for some authorities to accept. Evidence for the alternative theory – that they were transported to the vicinity of Stonehenge by glaciers (which would certainly account for the motley mix of rock-type) – is though, at the moment, not overwhelming, and the argument continues.

Perhaps round about the same time that the first stones were raised in the middle of the henge, four isolated sarsens, known as the Station Stones, were erected, just inside of the bank, on the corner points of a remarkably accurate rectangle which frames the central settings.

The form of the sarsen settings at the centre of the henge being established, work began on the main entrance. It was widened on the easternmost side and an approaching Avenue was constructed. The effect of this change was to shift the monument's alignment onto the axis of the midsummer sunrise and midwinter sunset. The, now recumbent (and colourfully named), Slaughter Stone is the sole remnant of a megalithic portal into the henge. Standing in the Avenue, but not on the centre-line, about 78 metres distant from the circle centre, is a massive (35 tons) unworked sarsen, called the Heel Stone.

Following the installation of the sarsen circle and trilithons, there was, apparently, some experimentation with the bluestones' positioning. They had been placed in a circle and horseshoe of uprights (no lintels), echoing the sarsen settings, by about 2100BC, and it is the remains of this final layout that is visible today. Placed within the horseshoe, near the closed end – at the heart of the monument – was the, so-called, Altar Stone: a, dressed, greenish sandstone block, some 6 tons in weight, of Welsh origin. The Altar Stone is recumbent today, and broken in two, pinned down by stones from the collapsed Great Trilithon. Opinion is divided over whether it was originally set upright or not.

Many years later, two, inaccurate, concentric circles of pits (the Y and Z Holes) were dug, outside the sarsen circle. They never received stones, and their, apparently, half-hearted construction, around 1600BC, seems to bring activity at Stonehenge to an end. By this time the sarsen settings had been in place for almost a millennium, and it is possible that some may have already fallen.

Built to inspire awe, Stonehenge was clearly a sacred place where rituals took place. Beyond that generalisation, however, its purpose and meaning have long been the subject of speculation. The SRP has found evidence supporting Mike Parker Pearson's theory that Stonehenge was but one component of a larger ritual complex. Durrington Walls, Britain's largest henge (around 480 metres in diameter), and, its smaller (around 85 metres in diameter) companion, Woodhenge lie in a little valley less than two miles to the north-east of Stonehenge. In 2005, a metalled roadway (Durrington Avenue) connecting the Southern Circle of Durrington Walls to the River Avon was discovered. Whereas Stonehenge and the Avenue were aligned on the axis of the midsummer sunrise and midwinter sunset, the Southern Circle and roadway were aligned on the axis of the midwinter sunrise and midsummer sunset. The timber structure of the Southern Circle was linked, via Durrington Avenue, the River Avon and Stonehenge Avenue, to the stone structure of Stonehenge. Professor Parker Pearson believes that the, short-lived, wooden structure represented the land of the living, whilst the permanent stones of Stonehenge represented the realm of the ancestors. Symbolic journeys between to the worlds of the living and the dead could be made via the monuments' ceremonial Avenues and the river.

Nobody ever lived at Stonehenge, but the remains of houses have been found at Durrington Walls: The houses are squarish and have floorplans similar to the famous stone built, late Neolithic, houses at Skara Brae, in the Orkneys. At Durrington Walls, where the houses would have been, predominantly, made from timber, none of the fixtures have survived, but there are slots in the chalk floor where the wooden furniture was located. The settlement may not, however, have been permanently occupied. The nature of the debris found in the houses, and the shortage of workaday implements, has led Professor Parker Pearson to suggest that it was occupied during a midwinter festival, when people from all over the region would congregate to take part in great feasts, and ceremonies involving the Durrington Walls/Stonehenge complex. The professor's theories are persuasive – he may be right – but, unfortunately, we can never know with certainty. As Samuel Pepys, having found the stones of Stonehenge “as prodigious as any tales I ever heard of them”, confided to his diary in 1668: “God knows what their use was”.

AVEBURY

Avebury is about 17, crow flying, miles north of Stonehenge. Even today its earthwork, enclosing an area 350 metres in diameter, is impressive. When built the bank would have been something like 27 metres wide at the base and 6 metres high. The ditch was 9 metres deep and some 14 metres wide at the top, tapering to less than half that at the bottom. There were entrance causeways at the north, south, east and west. These breaks in the earthwork were, millennia later, adapted to carry the roads serving the village of Avebury, which inhabits the henge. Some of the massive (in the region of 60 ton) stones that acted as portals can still be seen. Both remain at the southern entrance. One, the Swindon Stone, stands at the northern entrance. According to, antiquarian, William Stukeley, the Swindon Stone's partner (a stone “of a most enormous bulk”) fell down, and broke, in 1722: “... we saw three wooden wedges driven into it, in order to break it in pieces.” One fallen stone marks the eastern entrance. Nothing remains at the western entrance. The portal stones were part of a ring of standing stones which ran around the perimeter of the enclosed area. This outer circle (at the latest count) comprised 101 stones. 30 can be seen today. There were two inner stone circles, each roughly 100 metres in diameter. The southern one had about 30 stones set around the central Obelisk. Five stones from the circle still form an impressive arc. The Obelisk is no more. However it was sketched by William Stukeley in 1723. To the west of the Obelisk are a line of 6 smallish stones – the remains of the, so called, Z Feature. There were 9 stones in the line originally, and 3 other stones (one at the northern end, two at the southern) are known to have extended the setting, eastwards and inwards, towards the Obelisk. The eastern side of the southern circle has never been fully investigated. To the south of the circle stood the Ring Stone. All that remains is a stump, but according to William Stukeley the stone (“not of great bulk”) had “a hole wrought in it”. Excavation has shown that the Ring Stone had replaced a larger stone which originally stood in the same hole. Only four stones from the northern circle can still be seen. It is possible that this circle wasn't actually a circle at all. It may have been a horseshoe – open on the south. Either way, at its centre was the Cove – three stones set in a U-shaped arrangement – which opened towards the north-east (in the general direction of midsummer sunrise). Two of the three stones still exist. In 2003, work was carried out to straighten the leaning stones, which were in danger of collapse. The mighty back-stone, which projects almost 4½ metres above ground, was found to extend more than 2 metres (perhaps as far as 3 metres) below ground. It could weigh up to 100 tons. OSL dating indicated that the stone was erected c.3000BC. All the stones at Avebury are sarsens – found locally, on the Marlborough Downs, a couple of miles to the east. They have been left in their natural state – not smoothed or worked to shape, as happened at Stonehenge. It seems, though, that, in the circles, the stones were set so that their, naturally, smoothest side faced inwards.

The chronology of Avebury is far from certain, but the order in which it seems that the various components may have been constructed is, perhaps, somewhat surprising. The above mentioned OSL date suggests that, at about 3000BC, the Cove was the first structure erected. The inner stone settings – the southern circle and Obelisk, and the northern circle/horseshoe around the Cove – were probably next, beginning around 2900BC. Radiocarbon assays, from antlers found on the ditch bottom, tend to place the earthwork in the period around 2550BC. The perimeter stone circle was probably erected after the bank and ditch were finished. Other odd stones were also later additions – including the Z Feature and Ring Stone, which were supported by chalk blocks taken from the ditch. Two avenues of standing stones were built (say 2400BC) approaching the western (Beckhampton Avenue) and the southern (Kennet Avenue) entrances of the henge.

Avebury's stones seem to have remained unmolested until the early-14th century. Then, perhaps because they were offending Christian sensibilities, some were tipped into pits and buried. In 1934, Avebury was bought by a rich archaeologist, Alexander Keiller (of the ‘Dundee Marmalade’ family). His intention was to restore the site to something like its former glory. He cleared away trees, undergrowth and rubbish. He removed fences, old barns, and derelict cottages. Indeed, he wanted to rid the henge of all buildings, and used to have houses demolished as they became vacant. Keiller's investigations along the western half of the outer circle brought to light several buried stones. He re-erected them in their original positions. Where he found a stonehole, but the stone itself was missing, he had the position marked with a concrete plinth. Trapped by one of the buried stones was a human skeleton. It was dated, by coins, to the early-14th century, and was identified as a barber-surgeon, by virtue of a pair of scissors and a medical-looking probe or lance. At the time it was thought he had been accidentally crushed whilst assisting with the burial of the stone, but a more recent recent examination of the skeleton seems to indicate that this was not the case. Maybe he was pinned to the ground and died of suffocation, or maybe he simply died and, for some reason, was buried with the stone. At any rate, the re-erected stone is known as the Barber Stone. Keiller had begun excavating the southern circle (discovering the Z Feature) when his work was interrupted, by the outbreak of the Second World War, in 1939. In 1942 the National Trust bought Avebury. When the war ended, Keiller's poor health prevented him from resuming his excavations, though he continued to live in Avebury Manor until his death, in 1955. In 2003, at least 15 buried stones, in the eastern half of the outer circle, were located by geophysical survey, but there are no plans to follow Keiller's example and re-erect them.

In fact, the stones which were buried were the lucky ones: By the time William Stukeley visited Avebury (1719–24) the destruction of the stones was in full swing: Kennet Avenue connected Avebury to a stone circle, almost 2 miles to the south, whimsically called the Sanctuary. William Stukeley witnessed the destruction of this monument in 1723–24. Beckhampton Avenue has been so thoroughly erased that doubt about its very existence began to creep in. John Aubrey hadn't registered it, and there was a feeling that it may have been a figment of William Stukeley's imagination. Stukeley (who was ordained in 1729) became convinced that the Druid religion was the antecedent of Christianity. Further, he developed the idea that: The Sanctuary, at the end of Kennet Avenue, formed the serpent's head, and Beckhampton Avenue formed the tail. No remains of Beckhampton Avenue were apparent however, and, since Stukeley did tamper with his earlier findings to make them fit his theory, it was no wonder that some archaeologists were sceptical that Beckhampton Avenue had ever existed. Stukeley was vindicated, however, when archaeologists found traces of it in 1999. Where, and how, it terminates is not known. Stukeley was “sufficiently satisfied” he knew where it ended – making it about the same length as Kennet Avenue. He was also sure, for two reasons, that its terminus wasn't a stone circle. Firstly, because it was the tail of the snake, and to have a circle would be “absurd”. His second reason is, rather more convincingly, that there was “not the least report of such a thing among the country people”.

In his diary entry for 15th June 1668, Samuel Pepys wrote: Silbury Hill is less than a mile to the south of Avebury. Essential works to stabilise the monument, carried out in 2007–8, gave archaeologists rare access to the Hill's interior. New datable material has been found, and, additionally, archive material has been reassessed. A picture of Silbury Hill's chronology is beginning to emerge. It was raised in three phases. The first two quickly followed each other, a couple of generations either side of 2400BC. (It may be, then, that Silbury Hill's commencement overlapped with Avebury's conclusion). Dating the third phase is proving rather more problematic. One model has it following hard on the heels of the previous two phases, whilst another places it later – around 2000BC. It is hoped that, when all the results from the newly found material are available, the story will become clearer. Silbury Hill has been excavated several times (indeed, it is the collapse of excavators' workings which necessitated the recent conservation work), but, despite the local tradition mentioned by Pepys, no burial has been found. Recently discovered letters, pertaining to an excavation carried out in 1776, reveal that, at a depth 95 feet, a 6 inch wide “perpendicular cavity” was found: Silbury Hill's purpose remains the subject of, frequently fanciful, speculation.