Chapter 2 – Ancient Engineering
The first major construction at Stonehenge was a circular ditch, with an internal bank and a smaller external bank, built about 3000 BC. Today the ditch and inner bank are visible as low earthworks in the grass, but the outer bank has largely been ploughed away. The ditch on the eastern side is deeper because this half was excavated in the 1920s.
There were two original entrances to the enclosure – a wide one to the north-east and a smaller one on the southern side. There are many more causeways and gaps in the circuit today, mostly the result of later tracks which once crossed the monument.
Set just inside the bank were 56 pits, known as the Aubrey Holes. About half of these have been excavated, and were marked in the 1920s with white concrete circles.
SARSEN TRILITHONS AND CIRCLE
The stones of the central cluster, brought to the site about 2500 BC, are of two types – the larger sarsens and the smaller bluestones. The sarsens were erected in two concentric arrangements.
The inner one is horseshoe of five trilithons (two vertical stones capped by a horizontal lintel). Of these, three complete trilithons still stand (one fell in 1797 and was re-erected in 1958), and two are partly fallen. Near the centre is the Altar Stone, which is mostly buried beneath the fallen stone of the tallest trilithon.
Around the horseshoe are the remains of the outer sarsen circle, capped with lintels. There were probably once 30 stones in this circle, but many have fallen and most of the lintels and a few uprights are missing from the site.
Documentary by a BBC engineer
From the BBC, here is a link to a video documentary by leading structural engineer and designer Cecil Balmond, He goes beyond the well known histories of three celebrated monuments: Stonehenge, the Taj Mahal and the Great Pyramid, to reveal the hidden geometry at their cores.
At each iconic structure he examines a fundamental form: at Stonehenge – the circle: the Taj Mahal – the square and the Great Pyramid – the triangle.Through the abstraction of these forms Cecil reveals the secrets that lie within their iconic design and discovers what these basic shapes can tell us about the sacred and religious, the spiritual and transcendent intentions of the buildings’ architects. On a global journey across structure and shape, Cecil also explores how these simple forms influence our lives.