Moving further along the path parallel with the central stones, visitors get a clear view of the way in which the larger sarsens have been shaped and fitted together. At most stone circles built at this time in prehistory, blocks of stone were left in their natural, rough state and simply raised upright, but at Stonehenge they were treated differently. The sarsens within the central settings have been carefully trimmed, sometimes to produce sharply defined rectangular blocks, and have also been shaped to produce simple joints that lock the stones tightly together. Some of the bluestones also show evidence of shaping and jointing, although in their current setting they all seem to have been freestanding.




What can be seen today are the ruins of the stone settings that were constructed over several centuries from about 2500 to 2000 BC. Once in place the huge sarsens do not appear to have been moved but, in contrast, the smaller bluestones may have been rearranged several times.




There are four concentric settings, two circles and two of horseshoe shape. Even after more than 4000 years of decay, these structures can still be recognized today. The outermost setting was originally a circle of 30 upright sarsens, capped by horizontal lintel stones. Of these 30 uprights only 17 still stand while only five of the lintels are still in place, leaving the best preserved section on the north-eastern side, facing the entrance to the enclosure. The surviving uprights are closely spaced, with gaps of less than 1,5 m. (5 ft) between the stones; there is a slightly wider gap between those that most directly face the main entrance.




The uprights and the lintels are locked together by means of a joint more commonly used in woodworking: the mortise and tenon. A protruding peg, or tenon, on the top of each upright fits into a corresponding hole, or mortise, hollowed out of the underside of the lintel. The ends of the lintels are locked together by tongue and groove joints (also derived from carpentry), where a vertical tongue fits into a corresponding vertical groove. The sophistication of this part of the structure is increased by the shaping of the horizontal lintels: these are not rectangular as might be expected, but gently curved on both inner and outer faces. If this outer circle – now much ruined – was ever complete, its lintels would have formed a perfect ring of stone suspended high and perfectly level above the ground.
Inside and concentric with these sarsens lay a circular setting of as many as 60 small, upright bluestones, the majority of which show no sign of having been worked or shaped. Within this circle, though, are two finely worked stones with mortise holes which were clearly shaped as horizontal lintels before being reused as upright pillars. This circle is now fragmentary.


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Moving inwards, the next setting was the most impressive: a horseshoe of 5 massive sarsen trilitithons (from the Greek for “three stones”). Each trilithon consisted of two huge closely spaced uprights and an equally huge horizontal lintel, locked together with mortise and tenon joints. Three complete trilithons still stand (although the one closest to the tarmac path was re-erected in 1958). Among their uprights are the biggest individual stones at Stonehenge, weighing well over 40 tonnes. As rough stones when first found, before they were so carefully shaped, they must have weighed considerably more. This sarsen horseshoe is an extremely sophisticated structure, as the individual trilithons were originally graded in height, with the tallest, known as the Great Trilithon, at the closed end of the horseshoe. Only one stone of this magnificent structure still stands, the tallest standing stone in Britain, over 7,3 m. (24 ft) high. Some of the trilithon uprights were decorated with carvings of daggers and axes made over 700 years after they were raised.




The innermost setting is another horseshoe, this time of bluestone pillars. There were originally 19 stones, larger than those in the bluestone circle and including a number that were elegantly shaped. Some bear evidence that they once had tenons, suggesting that they supported lintels, although not where they stand today.
Finally, at the closed end of the innermost horseshoe, in the shadow of the tallest trilithon and now partly buried beneath its fallen upright, lies a stone known as the Altar Stone. This is the largest of the non-sarsen stones, a greenish sandstone from south Wales.

Not only were the stones carefully shaped and jointed together but the two horseshoes, of sarsen and bluestone, were lined up precisely so that their open ends pointed directly towards the entrance to Stonehenge.