Just a few minutes walk from the Sacred Plot, on the south side of the river, is the site of Arminghall Henge, a neolithic timber monument that has been dated to around 2500 BC, although it may be even older. There isn't a lot to see there these days, save for a few dips in the landscape where banks and ditches used to be, but aerial photography clearly shows just how impressive the whole complex was.
Cropmarks in the soil indicate eight giant post holes, almost a metre in diameter, arranged in a horse-shoe shaped pattern, seemingly aligned to the setting of the sun at the midwinter solstice. Subsequent excavations revealed the posts to have been oak, and sunk more than two metres into the ground - which means that they could have easily stood to a height of six or seven metres.
Obviously, nobody really knows why the monument was built, or indeed, who built it. It dates from a time when man was coming to grips with agriculture, and to some extent, trying to tame nature - not always successfully - so perhaps it had some ceremonial or ritual significance connected to the seasonal cycle. Perhaps it was a political statement of an affiliation of local clans who wanted to impress and intimidate trading partners and rivals (County Hall is only a short distance away).
Or maybe it was a neolithic job-creation scheme.
I'd like to think it was something of all of these - religious, political, cultural - and by being positioned in the landscape as it was, facing the setting sun on the shortest day of the year, the idea was to harness the fading power and in some way store it for the future.
It seems somehow apt that in the same field where the henge once stood there is now an electric power station, and rows of pylons in attendance.