Stonehenge

Fifteen centuries of building

The first Stonehenge, from about 3000 BCE, was an earthwork: a circular bank and ditch about 110 metres across, with a ring of 56 pits known as the Aubrey Holes. The great stones came later. Sarsen blocks raised between roughly 2600 and 2400 BCE form the outer circle and the inner horseshoe of five trilithons, each a pair of uprights capped by a lintel. The smaller bluestones, brought some 230 kilometres from the Preseli Hills of west Wales, were set and reset several times. Building ended around 1600 BCE, but people kept using the landscape for centuries more.

The sourcing of the stones is now unusually well known. Geochemical work published in 2020 traced most of the sarsens to West Woods, about 25 kilometres to the north; a 2024 study traced the six-tonne Altar Stone not to Wales but to the Orcadian Basin of north-east Scotland, some 750 kilometres away. Moving them with ropes, sledges and timber was a project of social organisation as much as engineering.

The solstice axis

The monument opens to the north-east. Seen from the centre, the midsummer sun rises close to the Heel Stone, and the same line run backwards points at the winter solstice sunset, framed by the largest trilithon. The Avenue, a pair of low banks running from the entrance towards the River Avon, follows the axis. The alignment is real and measurable. What it was for is not.

The astronomical reading entered modern debate in the 1960s, when Gerald Hawkins argued from a computer analysis that the stones predicted eclipses, an idea archaeologists largely rejected. The excavations of the Stonehenge Riverside Project led by Mike Parker Pearson, at the nearby timber circles of Durrington Walls, found midwinter feasting and led to a different reading: Stonehenge as a place of the ancestors, with the solstice as a calendar of gatherings rather than a laboratory. Both readings keep the sky at the centre; they differ on whether anyone was measuring.

Heritage and today

Stonehenge was inscribed on the UNESCO World Heritage List in 1986, together with Avebury and associated sites. English Heritage cares for the monument, and open access at the solstices has become a modern ritual of its own. The site is protected as a landscape, not as a ring of stones: roads, barrows and the Avenue are part of the record.

What the evidence cannot settle

Three kinds of evidence meet at Stonehenge and do not always agree: the geometry of the stones, the finds in the ground and the speculation of later centuries. Geometry shows that the builders cared about the solstice axis, but it cannot say whether they watched the sky or celebrated it. The finds, including animal bones, cremation burials and the houses at Durrington Walls, speak of gatherings and of the dead. Later centuries added legends, from Merlin to Druids, that have no support in the record. A careful reader keeps the three apart. For an observing network the same discipline applies: record what was measured, what was inferred and what was assumed, and label each.

Instruments and technologies

• The solstice axis A sight line fixed in earth and stone: the entrance, the Avenue and the Heel Stone line up on the midsummer sunrise, and the trilithon horseshoe frames the midwinter sunset. It works with no moving part: the sun does the moving.
• Sarsen circle and trilithons Thirty uprights carried a continuous ring of lintels at a constant height, joined with mortice-and-tenon and tongue-and-groove joints, a carpentry technique applied to stone.
• Station Stones Four stones set in a rectangle whose long sides parallel the solstice axis, interpreted by some as markers for the moon's extreme risings.

The people

• Gerald Hawkins Astronomer whose 1960s analysis made Stonehenge a case study in archaeoastronomy.
• Mike Parker Pearson Archaeologist who led the Riverside Project and argued for a monument of the ancestors.
• Alexander Thom Engineer whose surveys of British stone circles shaped the debate on megalithic astronomy.

Timeline

• 3100 BCE Earthwork bank and ditch dug, the first phase of the monument.
• 2600 BCE Sarsen circle raised, between about 2600 and 2400 BC.
• 1600 BCE Construction activity ends, around 1600 BC.
• 1986 Inscribed on the UNESCO World Heritage List.

Key lessons for observation today

• An alignment is evidence, not proof A line that points at the solstice sun is easy to find and hard to interpret. Modern observing networks record why an instrument is where it is, how it is oriented and what it was meant to see, so later users do not have to guess.
• Record the survey, not only the data Stonehenge survives as geometry because the builders fixed it in stone. A modern site survives as a record when its location, orientation and datum are written down in machine-readable form.
• Sites last when they are cared for as places The monument outlived its builders because later generations kept using and protecting the landscape. Long-lived observing sites need an owner, a steward and a plan for access.

Sources

• Wikipedia, Stonehenge
• English Heritage, the stones of Stonehenge
• UNESCO World Heritage Centre, Stonehenge, Avebury and Associated Sites
• Nash et al. (2020), Origins of the sarsen megaliths at Stonehenge, Science Advances
• Clarke et al. (2024), Stonehenge Altar Stone from the Orcadian Basin, Nature