Spiralling into the minds of our Stone Age ancestors

The Stoney Littleton long barrow in Somerset, England.

When the Stoney Littleton long barrow was constructed about 5,500 years ago, its builders used a stone with a splendid spiral ammonite fossil embedded in it to mark the entrance.

Why did they do this? The ammonite cast, about twelve inches in diameter, is distinct on the lower wall, or jamb, of the portal — you can see it in my photo above, at ground level on the left-hand…