Y and Z Holes
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The Y and Z Holes are two rings of concentric (though irregular) circuits of 30 and 29 near-identical pits cut around the outside of the Sarsen Circle at Stonehenge. The current view is that both circuits are contemporary. Radiocarbon dating of antlers deliberately placed in hole Y 30 provided a date of around 1600 BCE, and a slightly earlier date was determined for material retrieved from Z 29.[1] These dates make the Y and Z holes the last known structural activity at Stonehenge.
The holes were discovered in 1923 by William Hawley, who, on removing the topsoil over a wide area, noted them as clearly visible patches of "humus" against the chalk substrate.[2] Hawley named them Y and Z because for a short time he had earlier labelled the recently discovered Aubrey Holes as the X holes.
18 of the Y Holes have been excavated, and 16 of the Z Holes. Further evidence of the Y and Z Holes being late in the sequence of events at Stonehenge is demonstrated by the fact that hole Z 7 was found to cut into the backfill of the construction ramp for stone 7 of the Sarsen Circle.
