The bulldozers had been clearing jungle for days, their crews hacking through the dense brush of Costa Rica’s Osa canton to make room for banana plantations. Then the workmen hit something strange. Buried in the earth, half-hidden by roots and undergrowth, were enormous stone balls, perfectly round and smooth, sitting in clusters as if someone had deliberately placed them there. At first, the men were merely puzzled.

The United Fruit Company’s machinery was not gentle, and some of the spheres were shoved aside, cracked, or crushed outright as the heavy equipment rolled over them. But once the workers got a closer look, their confusion turned to excitement. They decided the balls had to be hiding something valuable, gold probably, sealed away inside the rock. So they rigged some of them with dynamite and blew them open.

They found nothing but stone. Solid, unbroken stone, through and through. Still, they kept at it, blasting sphere after sphere apart, convinced the next one would reveal its treasure. It took the intervention of authorities to stop the destruction.

And only then, once the dust had settled, did archaeologists begin to realize what had actually been found. These were the bolas de piedra, the stone spheres of Costa Rica, and there were hundreds of them. In total, roughly three hundred of the spheres were accounted for. Most were carved from gabbro, a coarse-grained rock similar to basalt, though a few were made of limestone and a handful of sandstone.

Their sizes varied enormously. The smallest measured just two centimeters across, little more than a pebble. The largest stood two meters in diameter, a solid ball of stone weighing up to fifteen tons, heavier than an African elephant. And all of them, every single one, had been shaped by hand.

The people who made them had no metal tools, no modern carving equipment. Each sphere was produced through meticulous hammering with stone implements, then laboriously polished smooth, a process that likely consumed tens to hundreds of hours per ball. And once finished, the spheres had to be moved, dragged across the landscape to wherever they were meant to rest, a task that defies easy imagination given their weight. The question of who had done all this work pointed to the Diquis people, a pre-Columbian indigenous group who inhabited the delta of the Terraba River and the small Cano Island, roughly sixteen kilometers off the western shore.

They were a subsect of the larger Chiriqui culture, which stretched from Costa Rica into Panama. But beyond that, very little is known about them. No population numbers, no detailed cultural record, no clear timeline. Most of what scholars understand about the Diquis comes from the spheres themselves, and the spheres have refused to give up their secrets.

No one has been able to determine why they were made. Hypotheses have ranged from the practical, that they were a way for the ancient population to pass the time, to the spiritual, that they served religious purposes, to the frankly mundane, that they were lawn ornaments for the powerful elite. What little other evidence exists only deepens the mystery. The Diquis built mounds and public plazas, and small statues have been found bearing feline and lizard faces, suggesting those animals played a significant role in their society.

But that is nearly all there is. One day they were making balls. The next, they stopped. Dating the start and stop of the spheres’ production has proven difficult, largely because the places where the spheres were found differ from where they were originally made.

The earliest proposed date suggests they began appearing as far back as 300 BC, roughly 2,300 years ago, and continued up to the sixteenth century. Interestingly, from about 1,300 years ago onward, the Diquis seem to have produced them at an accelerating pace, until production simply ceased. The end of the Diquis coincides disturbingly well with Spain’s colonization of Costa Rica. Yet no European explorer of that era ever mentioned the spheres in any written account.

More tellingly, an expedition that passed directly through the region where the Diquis had lived reported no spheres, and no signs of human life or settlements at all. By the time the Spanish arrived, the Diquis appear to have already died out or abandoned their homes. Did they see the conquistadors coming and flee? Were they wiped out by introduced diseases?

Or did something else entirely drive them away? Like the purpose of the spheres, no one knows, and probably never will. Not all such mysteries carry such a somber ending, though. Sometimes they are just strange.

In the 2020s, a team excavating a forest in the northeastern Indian state of Assam made a striking discovery: giant jars, sixty-five of them, carved out of sandstone. Sandstone is a sedimentary rock made up of sand-sized grains of silicate cemented together by other minerals, which makes it relatively easy to carve compared to harder stone, though that ease is only relative. Some of these jars stood three meters tall and weighed over ten tons. Unlike the Costa Rican spheres, which could at least be rolled, jars of this size would have been a nightmare to move, and whoever built them must have been remarkably strong.

What made the find even more puzzling was that local civilians had known about the jars for generations. Civil servants had described them as far back as the 1930s, though no one had paid them much attention until the recent excavation. Dating attempts yielded mixed results, with the only firm conclusion being that the jars were all over 2,400 years old, dating to before 400 BC. Some local group in the region must have dug them out of the earth, but who, and why, remains unclear.

Jars today are mostly used for storage, of food and other items, and it is certainly possible the Assam jars served that purpose. But jars meant for storage tend to be much smaller. And it was not just the original sixty-five. Since the first discovery, researchers have located at least 640 more, bringing the total to over seven hundred giant jars scattered across just four sites in Assam.

When researchers cannot figure something out, their default hypothesis tends to be burial practices. There is some indirect evidence for this. In Laos, jars of similar size have been found containing human remains, more than two thousand of them, with bones and other items both inside and around the jars. But the Assam jars are different.

Of the seven hundred studied, not a single one has been found to hold anything of significance. No bones, no personal belongings, nothing. Except for one tidbit: in a single report from the 1930s, someone claimed that one or two of the jars did contain bones. That is all.

Still, the burial theory persists, though it leaves ample room for doubt. It is just as possible that this ancient civilization simply had a thing for giant jars. There is another answer to the question of why ancient people did strange things, and it is one most people will recognize: boredom. Take doodling.

A doodle is any drawing made while a person’s attention is occupied elsewhere, and doodles tend to be simple, random, and more frequent when someone is bored, daydreaming, or procrastinating. It turns out doodling has been in the repertoire of people who should be doing something else for a very, very long time. The earliest confirmed example comes from South Africa’s Blombos Cave, a site dating to between 100,000 and 70,000 years ago, during the Middle Stone Age. The cave has long been a treasure trove of archaeological importance, yielding bones, shell beads, stone tools, and bone tools, all suggesting it was inhabited or at least frequently visited by anatomically modern humans.

Among these important finds was a rock. Just a rock, but with red lines all over it. Nine red lines, to be exact, arranged with no visible pattern, just lines upon lines. At first glance it might have been dismissed as nothing, but the red coloration was unusual, and researchers suspected the markings were man-made.

So, despite the risk of finding nothing, they spent the next seven years studying the rock extensively. Their patience paid off: the red lines were undoubtedly human work, made with a red ochre crayon. The rock is 73,000 years old. The lines stop abruptly at the corners of the rock, suggesting that when the artist made the doodle, they did so on a larger piece of stone.

What they were drawing, and why, is unknown. The current belief is that whoever did it simply doodled for the sake of doodling. That unknown artist holds the title for the oldest doodle by Homo sapiens, and for the first known case of modern humans drawing in any capacity. But it was not only our species that had this streak of randomness.

There is a potential case of a Homo erectus dabbling in abstract art, far earlier than researchers once thought possible. It has to do with a Pseudodon, which, despite the name, is not a mammoth-like animal but a freshwater mollusk still living in Southeast Asia. The specific shell in question dated back 485,000 years, to the Chibanian stage of the Middle Pleistocene, and was found at Indonesia’s Trinil site along the banks of the Bengawan Solo River. Trinil is a well-established trove of paleoanthropological finds, home to the famed Java Man, and has long been known to have hosted various groups of Homo erectus, a species famous for being first at many things, such as building houses.

But art was long thought to be beyond them. Until this shell. Its zigzag lines appeared to have been deliberately made, engraved in a single session. Based on the impressions and the shell’s association with a coastal community, researchers believe the tool used was a shark tooth, a common implement for opening shells.

The discovery kicked up a fiery debate. For a long time, such an action was considered outside the realm of possibility for Homo erectus, given assumptions about their cognitive abilities. Questions followed: How smart were they really? Were there other cases of them being goofballs?

And what was the function of a zigzag shell? No one knows. Some believe it was simply a thing someone did out of boredom, much like picking up a shell and doodling on it. Others speculate it was a territorial marker, though how terrifying a graffitied seashell really is remains debatable.

Some suggest it was an attempt to impress a fellow Homo erectus. And then there are those who think the shell was a deliberate art piece, the zigzag carrying some deep symbolic meaning, perhaps representing the ups and downs of life. The simplest explanation, that an erectus was bored one day, is probably the right one. But no one will ever know for sure.

Not every find that reflects human randomness has to do with doodling. Some people are more into making things than marking them. Researchers are aware of the Acheulean hand axes, associated with Homo erectus, Homo heidelbergensis, and even early Neanderthals. The Acheulean industry began as far back as 1.

95 million years ago, during the Lower Paleolithic, and continued until just 130,000 years ago, with traces found across Europe, Africa, Asia, and possibly parts of Australia. It is considered the longest-running culture in human history. Its chief product was the handheld stone axe: oval or pear-shaped, used for butchering, cutting wood, digging roots, and scraping material. It was often nicknamed the Swiss Army knife of the Stone Age.

But just as someone can own so many knives that it raises questions, researchers have discovered sites with abnormal accumulations of axes. The most striking is the Olorgesailie Basin in Kenya, located in the Eastern Rift Valley. First stumbled upon by modern scientists in 1919, it only drew real interest in the 1940s, when researchers found multiple extinct species of animals, including hippos, elephants, zebras, giraffes, and baboons, all showing distinct signs of having been butchered by humans. But what was truly off was the sheer number of axes.

Buried there were not hundreds, but thousands upon thousands of them, the highest concentration of axes on the planet, out-axing anything found in ancient armories from the Romans to medieval barracks. Thousands have been sent to museums around the world, and still thousands remain buried. And then there were the other perplexing finds. The vast majority of the axes showed little to no signs of use.

They were, figuratively speaking, squeaky clean, odd for tools that were used for everything. And if you find thousands of axes in an area inhabited by people, you would expect to find some skeletons. Perhaps thousands, hundreds, or at the very least tens. Instead, researchers found just one, and even that was incomplete: the partial, fragmented frontal bone of a 950,000-year-old Homo erectus.

This was the most striking case, but not isolated. At least two other sites, including some in Europe, show the same pattern: abundant axes, never used, with no human remains nearby. The most popular hypothesis is that these sites were factories, production centers from which axes were transported over long distances. But there are problems with this.

Many of the axes were highly symmetrical, meticulously crafted, and would have required exceptional time and effort to make, not what you usually see in factories, where quantity and effectiveness are the priority. Studies have found that much cruder axes would have performed just as well. None of the axes showed signs of being tested after production, or of being moved around, and there were no clear production zones, no designated areas for various stages of work or for waste, as you would expect in a factory. What’s more, these kinds of sites are unique to the Acheulean.

Nothing like them, mass-produced symmetrical tools, is seen anywhere else in the archaeological record. This has led to another idea: that the hand axes were not factory products at all, but something closer to a prehistoric hobby. And that the large piles represent less a manufacturing center and more someone standing back and admiring their collection. It is impossible to know for certain.

But it goes to show that while the world around us has changed, perhaps humans themselves have not changed so much after all.