The term 'henge' is
being increasingly used to defined a variety of structures built
between 3000-5000 years. These take the form of banked
enclosures, stone chambers and separate stones arranged in avenues
and circles. Some circles have very complex geometry and the
local astronomy of the site was often built into the
design.
Neolithic farmers
appeared first appeared in Britain around 4000BC and by 3000BC the
first megalithic (large stone) constructions started. There are
several types of stone structures, the simplest being the raising
of single, sometimes massive, standing stones called menhirs.
Hollow box-like structures made from large stones were used for
burials and covered with mounds of soil, these are called dolmens
or, in Wales, cromlechs . Cairns are cromlechs covered in stones
and barrows are earthen burial mounds. Henges are usually stone or
vertical timber circles often surrounded by a ditch and bank.
Most stone circles were constructed in the late Neolithic to early
Bronze Age periods. They occur all over the UK except in the
southeast where there is no evidence of them, but this does not
mean there were none. Many stone circles have been removed and
recycled in walls and buildings or cleared for farming. They
survive best where there has been little development. Stone circles
are also found in parts of Europe.
Early circles, or
henges, were made from wood, both Woodhenge and Stonehenge are
examples of these. Stone was used for permanence and local
materials were generally used but sometimes stones were transported
great distances. The proximity of circles to burials suggests they
were built with some significance to the dead or to hold ceremonies
as well as being "calendars" lined up with astronomical features
such as solstice sunrises, moonrise and moonset and specific
constellations.
Following detailed
surveys of hundreds of sites, Alexander Thom, a professor of
engineering at Oxford, concluded that the megalithic builders used
a standard unit of measurement. This unit was 2.72 feet
(0.83m), the megalithic yard, about the size of a pace except that
over all his surveys he shows there is only a deviation from
proportions of this dimension of only 0.003 feet! His findings show
the builders used whole or half units of megalithic yards in the
radii of stone circles. Many structures include extremely accurate
alignments with key solar and lunar risings and settings, often
using natural features like mountain peaks, notches in hills or the
strategic placement of standing stones as precise sightlines. These
astronomical alignments were an integral part of the design of many
sites. The geometry of the non circular stone circles was not by
accident or inaccuracy but was based on complex ellipse or
flattened circle geometric construction.
Solar symbols are
common in megalithic tombs, the role of the sun would have been
important to Neolithic farmers as crops and cattle depended on it.
Stones placed in a circle were sighted to show the occurrence of
the summer and winter solstices. In the winter in the northern
hemisphere the sun rises in the southeast and stays low in the sky,
setting in the southwest. During the spring and summer these
positions shift farther north along the horizon and the sun stays
in the sky longer. Some tomb passages were aligned so that the
rising sun of the winter solstice would shine down them. This would
represent the start of the lengthening of the days and the start of
the growing season being a cause for celebration.