The Bone With Twenty-Nine Cuts

So this is not a pattern cut in one afternoon. Someone came back to the bone more than once and added to a row that already meant something to them. The 2018 study calls it the earliest known example of a notation that was added to over time. That is what the microscope can show. It cannot show what the notches stood for. A notch for a night, an animal, a person or a promise looks the same under the lens.

The moon question

Here is the case for the moon, put as strongly as it deserves. The Moon goes from one full moon to the next in about 29.5 days: 29 days, 12 hours and 44 minutes on average. For people with no written calendar, its changing face is a clock anyone can read. A bone with 29 marks, kept and handled for a long time, sits remarkably close to that number. And notched sticks are no stranger here: the 2012 study lists notched sticks used as counting systems among the familiar parts of San hunter-gatherer culture, the very culture it traces back to Border Cave.

The moon idea also has a long history. In 1964 Alexander Marshack, a journalist who taught himself prehistory, published the first of many studies arguing that marks on Ice Age bones recorded the phases of the Moon, and his 1972 book The Roots of Civilization carried the idea to a wide public. One of his favourite examples is a small bone plaque from the Abri Blanchard in France, more than 30,000 years old, covered in 69 small pits. Marshack counted 24 changes of tool among them, and read the winding line as a record of the Moon waxing and waning.

Now the case against. The bone is broken and the row is incomplete, so 29 is the number that survived, not necessarily the number that was cut. The microscope shows the notches went on in batches of very different sizes, eight at one sitting and fourteen at another, with single notches squeezed in later. A strict one-notch-a-night tally would more naturally grow one mark at a time, though a careful keeper could have caught up in batches. Nothing else in the layer ties the count to the sky. And Marshack's critics long complained that, given enough assumptions, he seemed able to find a lunar cycle in almost any set of marks.

That leaves us where the evidence ends. The notches are real, the changes of tool are real, and the count was kept over time. The moon is a hypothesis built mostly on one number from a broken object. That is why this stop carries the rating Speculative: not because the idea is foolish, but because nothing found so far can prove it or rule it out.

A cave with a long memory

Border Cave is a rock shelter high on a cliff in the western Lebombo Mountains, in KwaZulu-Natal, close to the border with Eswatini. It sits about 600 metres above sea level, and its mouth looks west over the Eswatini lowveld. People have dug here since Raymond Dart's first trench in 1934, and a team led by Lucinda Backwell, Lyn Wadley and Francesco d'Errico reopened the excavations in 2015.

Its record is unusually long. The deposits, alternating bands of brown sand and white ash, run from about 227,000 years ago to about 24,000 years ago, and some luminescence dates push the bottom towards 250,000. About 200,000 years ago, people here were laying grass bedding on top of ash, perhaps to keep crawling insects away, and a 2026 study of the beds under the microscope traces their building and upkeep all the way to 43,000 years ago. About 170,000 years ago they were roasting the starchy rhizomes of Hypoxis, the yellow star flower, in their fires.

The layers around the notched bone, from about 44,000 to 42,000 years ago, hold some of the cave's most remarkable finds. There are thin bone points much like the poisoned arrowheads of San hunters, one carved with a spiral groove filled with red ochre, close to the marks San hunters use to tell whose arrow is whose. There are beads of ostrich eggshell and marine shell, a digging stick of white-berry bush wood, and a lump of beeswax mixed with Euphorbia resin and bound with plant fibre, dated to about 40,000 years ago and the oldest known use of beeswax. Three other notched bones come from the cave too, so marking bone was not a one-off. And in 2022 the team reported the remains of a child of three or four, from a layer dated to about 42,600 years ago, close to the notched bone's own age.

For the 2012 team, these finds pushed the start of a recognisably San way of life back to about 44,000 years ago, more than twice the 20,000 years most archaeologists had assumed. Around the cave itself, the bones of small mammals suggest savanna woodland and lowveld between about 50,000 and 24,000 years ago. Whoever cut the notches lived among people with poison, glue, beads and digging sticks. Border Cave is a protected heritage site today, with a small site museum that visitors can see if they book ahead.

Not the only notched bone

The Lebombo bone is often mixed up with the Ishango bone, and it is easy to see why: both are African, both are notched bones, and both have been read as counts of the Moon. But they are far apart in place and time. The Ishango bone was found in 1950 by the Belgian geologist Jean de Heinzelin on the Congolese shore of Lake Edward, in Central Africa, about 3,000 kilometres north of Border Cave. It is nearly 20,000 years old, less than half the age of the Lebombo bone, has a fragment of quartz fixed in one end, and carries 168 notches in three columns. It lives in Brussels, at the Royal Belgian Institute of Natural Sciences, and it is the next stop on this tour: Three Columns by the Lake.

Older than both is a fragment of hyena thigh bone from Les Pradelles in France, between 72,000 and 60,000 years old, carrying nine deep incisions that a Neanderthal seems to have cut in a single sitting. The 2018 study suggests it too may record numbers, but made all at once, not added to over time like the Lebombo bone. Later people kept other counts that have also been read as moons: a row of dots under a painted stag at Lascaux, and an arc of twelve pits at Warren Field in Scotland. Each reading is still argued over.

From a notch to a date window

Whatever the Border Cave notches counted, the act itself is familiar: one mark for one thing, added as it happens, kept so it can be read later. A watch with a date window does a mechanical version of the same job. Inside, a date disc moves on by one each day, shifting around midnight, so the count of days is kept for you. Some watches go further and show the phase of the Moon, the same 29.5-day cycle that someone may, or may not, have been following on a baboon's bone.

No one alive knows what was being counted at Border Cave. But somebody thought it worth coming back to the same small bone, again and again, to add one more mark. Every date window carries on that idea, whether or not the Moon was ever part of it.