may also have been dug out and refilled numerous times. The holes are in an accurate, 271.6m circumference circle, distributed around the edge of the area enclosed by Stonehenge's earth bank, with a standard deviation in their positioning of 0.4m. The circle they describe is around 5m inside the monument's bank. Twenty-one of the holes remain unexcavated and no reliable dating material has been recovered from the other thirty-five. The only available carbon date from the holes comes from charcoal in one of the later cremations. It gives the broad range of 2919–1519 cal BC. That sarsen stone chips have only been found in the upper fills of the excavated pits implies that the digging of the holes predates the megalithic phases of Stonehenge. From this stratigraphic evidence it is therefore likely that the holes were dug during the first phase of the monument, Stonehenge 1 (around 3100 BC) and were then reused for burials during Stonehenge 2 in successive centuries. By the time the standing stones of Stonehenge 3 were erected (around 2600 BC), the holes had fallen out of use. The positions of the holes are today marked at the Stonehenge site by white discs laid in the ground surface. Archaeologists number them 1 to 56 counting clockwise from the later Slaughter Stone at the eastern side of the north east entrance. Hawley reburied the human cremations he found, placing them in the backfilled hole number 7. These remains were re-excavated in August 2008 as part of the Stonehenge Riverside Project. A plaque dating from the 1935 reburial was uncovered at the site. The project was detailed in an episode of the PBS TV series Nova around the same time. Theories about the holes Many interpretations prefer an astronomical explanation for the purpose of the holes although this is by no means proved. It was formerly thought that when the Aubrey holes were first dug, the only standing feature at Stonehenge was the Heelstone, which marked the point of the midsummer sunrise, viewed from the centre of the henge. But the Heelstone is now attributed to Stonehenge 3 and was therefore not contemporary with the holes. It has been suggested that the Aubrey holes were originally intended to be postholes containing timbers or stones but this is uncertain. Analogous timber circles at sites such as Woodhenge have influenced this interpretation; the positioning of the Aubrey Hole circle relative