Stonehenge maybe, in many peoples' minds, the most mysterious place in the world. This set of concentric rings and horseshoe shapes on the empty Salisbury Plain, is, at the age of 4,000 years, one of the oldest, and certainly best preserved, megalithic (that means large, often ancient, stone) structures on Earth. It is a fantastic construction with many of the larger stones involved weighing 25 tons and quarried from a location 18 miles away. The rings and horseshoes of Sarsen (a type of sandstone) also carry massive lintels connecting them so that when they were all in place there was a ring of stone in the sky as well as on the ground. We know almost nothing about who built Stonehenge and why. A popular theory advanced in the 19th century was that the Druids, a people that existed in Britain before the Roman conquest, had built it as a temple. Modern archaeological techniques, though, have dated Stonehenge and we now know that it was completed at least a 1,000 years before the Druids came to power. If Druids used Stonehenge for their ceremonies they got the site secondhand. Despite this, modern Druids have laid claim to Stonehenge and an annual ceremony takes place at Stonehenge during Summer solstice, one of the ring's astronomical alignments. There is evidence there was activity on the Stonehenge site as far back as 11,000 years ago. It wasn't until about 3100 BC, though, that a circular bank, following the current Stonehenge layout, appeared. At the same time pine posts were put into place. Around 2100 BC stones started being erected. First bluestones from Wales, then the larger Sarsens stones. During this period some stones were erected, then later dismantled. Why did the builders create, dismantle and rebuild this isolated site? It's hard to say. They apparently didn't have a written language and left no records. We can say one thing about Stonehenge based on archaeological digs at the location. There is almost no "trash." A nu...