Watch clips from the Stonehenge episode of Timewatch

The great and ancient stone circle of Stonehenge is unique; an exceptional survival from a prehistoric culture now lost to us. The monument evolved between the later Neolithic period (c. 3000 BC) and the middle of the Bronze Age (c. 1600 BC), and is aligned with the rising and setting of the sun at the solstices, but its exact purpose remains a mystery. Over many centuries, there has been intense debate about the significance and uses of Stonehenge. Certainly it became the focal point of a landscape filled with prehistoric ceremonial and burial structures. It also represented an enormous investment of labour and time. A huge effort and great organisation was needed to carry the stones tens - and sometimes hundreds - of miles by land and water, and then to shape and raise them.Only a sophisticated society could have mustered so large a workforce, and produced the design and construction skills necessary to build Stonehenge and its surrounding monuments. Stonehenge's orientation in relation to the rising and setting sun has always been one of its most remarkable features. Yet it remains uncertain whether this was because its builders came from a sun-worshipping culture or because - as some scholars have asserted - the circle and its banks were part of a huge astronomical calendar. What cannot be denied is the ingenuity of the builders of Stonehenge.With only very basic tools - such as antler picks and bone 'shovels' - at their disposal, they dug the enclosing ditch and erected the bank, later using similar tools to dig the holes for the stones.Other stone tools were used to shape the mortises and tenons that linked uprights to lintels. Some of these tools can be seen, together with other artefacts including personal material from graves, on display in the museums at Salisbury and Devizes. The first monument in the Stonehenge landscape consisted of a circular ditch and bank (c100m in diameter), possibly with a ring of 56 wooden posts, the pits for which are now called Aubrey Holes. Some 4-500 years later the first stones arrived: these were bluestones, transported over 240 miles from the Preseli Mountains in Pembrokeshire. Paired bluestones were erected in an arc to the north east of the centre of the monument. Shortly afterwards this was dismantled, and replaced by an arrangement of stones which included the much larger super-hard sarsens, from the nearby Marlborough Downs. The outer circle was composed of 30 sarsen uprights with a similar number of lintels: this enclosed five sarsen trilithons (pairs of uprights with a lintel across each), arranged in a horseshoe shape, with the open end towards midsummer sunrise. Bluestones were re- erected in a circle between the outer sarsen circle and horseshoe, and inside the horseshoe. Some bluestones were later removed to leave the final setting, whose remains can be seen today. In the landscape immediately around Stonehenge there are visible remains of many different types of monuments, and many more have been detected. Neolithic monuments include long barrows, and the long oval earthwork to the north, the Cursus (once thought to resemble a chariot racecourse): together with the henge monuments at Woodhenge and Durrington Walls, contemporary with the early phases at Stonehenge. The most numerous monuments are the remains of Bronze Age round barrows, which are contemporary with the later phases of Stonehenge. Stonehenge is surrounded by 1,500 acres of land owned by The National Trust, with excellent walks to some of the monuments mentioned above.

The first excavation inside the stone circle at Stonehenge in nearly half a century

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