The first glimpse often comes from the road. Blurring past on the A303 thoroughfare that cuts heedlessly almost across the monument’s very entrance, Stonehenge appears as a cluster of insignificant protrusions on the big, otherwise featureless plain; and yet, even from this profane and glancing vantage, the great-shouldered silhouette is so unmistakably prehistoric that the effect is momentarily of a time warp cracking onto a lost world.