A bit today about the Pallisades at Avebury.
In between Silbury Hill and The Sanctuary there existed an area we know today as The Pallisades, which is probably the most unknown feature of the area but was possibly more impressive than Avebury itself in its day. It has been dated to around 2,500 BC, so it is contemporary with the henge and Silbury. As the name suggests, this was two enormous circular enclosures containing a number of complex features we know nothing about.
To give some idea of the scale of The Pallisades, some 2,000 wooden posts were erected. Each post was about a metre across and may have been 6 to 8 metres high, as estimated by Whittle in 1997.
One of the enclosures straddles the River Kennet, which winds down from the north above Silbury, going some way the south of it before taking an abrupt turn the north east. The other sits just south of the river.
The fields are all ploughed out, but painstaking work by Pete Glastonbury and Steve Marshall plotted the crop marks seen at various times among the cereal crops.
It was Pete who first drew attention to Silbaby, indeed he gave it its name, which seems to have stuck. Silbaby sits adjacent to these Pallisades. A map is in order:
Together with an archaoastronomer, George Currie, the team did some research on what are called sunrolls at Silbury.
Sun and moon rolls occur in places where a slope of a hill, mountain or artificial features can be seen against the horizon. They are starting to be recognised at many megalithic sites, but of course the sighting point has to be known as well - a backsight.
In the case of the sun, a hill with a slope of between 30º-35º will roughly be at the same slope as a rising or setting sun at these latitudes.
Now it just happens to be the case that a pile of dirt, be it chalk or gravel, will tend to settle at about this angle naturally. Silbury has been analysed and may actually be nine-sided, Field, 2008. Generally it slopes about 30º. Ideal candidate for a sunroll.
I will divert just a second to say a word or two about Silbaby. Whether Silbaby is natural or man-made we don't yet know but whatever the case, there is a spring which starts at the base of Silbaby and curves under it to meet the River Kennet. This may have been significant for those living in The Pallisades.
The sketch below is a little misleading, Silbaby stretched across the road to the north and was cut across its northern side, so it was probably a little bigger than shown here and thus slap bang on the line between The Sanctuary and Silbury. Stukeley and others certainly noted Silbaby on their plans as a feature worthy of note.
What was found is that a sunroll viewed from The Pallisades shows the sun rolling down Silbury Hill, where it disappears framed by Silbaby into the source of the spring.
This is the view to Silbury we are speaking of, Silbaby at right:
Picture below by Pete G, who regrettably is now unwell and unable to do much further research on this. He hoped to publish this work, but now says this is unlikely. The view is from about where it says structure 3 in the plan at top.
The sun rolls down the slope of Silbury and plops into the spring around May Day. The picture shown here is May 16th 2009. May 15th was optimum but cloudy. The sun moved north and returned again as predicted for an optimum roll again on July 25th.
The moon follows a similar arc, so moonrolls could feature viewed from here also.
Want to go down there and investigate Richard? Sunset of the 25th?