It's curious to consider the progression of the human species. Hominins--human-like apes--didn't appear on Earth until about 7 million years ago. The homo genus first appeared about 2 million years ago. Homo sapiens showed up maybe 200,000 years ago. Humans didn't start settling down in any permanent way until 12,000 years or so ago. Even then, it was only isolated bands of a couple hundred people at most, in places that supported cultivation of the soil and had domesticable plants--and, of course, the human knowledge to take advantage of those features.
Human technology and culture exploded after that. Within a couple thousand years, the first cities had formed. Far more than villages, these supported thousands of people. With no precedent for how to build cities, those first city-dwellers had to make it up as they went. They had not yet conceived of streets, nor public buildings. Instead, rectangular structures of plaster and stone were put up, sharing walls and floors and ceilings, and were stacked on top of each other. Their only ventilation came from ladder shafts which also allowed smoke from hearthfires to escape. If they gathered in an open space, it was most likely on the roof of the entire structure. Sanitation must have been an early discovery, as garbage was kept away from the living areas. There were many signs of culture, too: wall paintings, animal heads and skins, clay figurines. Writing was still a ways off, but putting marks on walls has been a human activity for about 65,000 years.
If the city needed to expand, it could grow up and out. Sometimes, the city would be structurally compromised or would be abandoned. In such cases, the entire city would be demolished and then rebuilt. Imagine destroying and rebuilding your city every ten years or so! Unfathomable. And they built directly on top of the ruins of the previous incarnation--perhaps because the bones of their relatives were buried there, too. Sometimes a valued part of a relative, such as their skull, would be adorned with clay and stones and even gems to make it appear lifelike again, placed prominently in the home, as if to suggest they aren't really gone.
Why did people choose to live this way? Hunting and gathering had sufficed for millions of years. Millions! The need for food may have been paramount. It is perhaps not a coincidence that humans began settling down and farming around the same time we drove almost all of the last megafauna to extinction. Hunting smaller animals wasn't worth the expenditure of energy, nor could the deficit be made up simply through extra gathering of berries and acorns. Farming, though--farming changed everything.
If you were going to stay in one place and grow crops, that meant you had to actually stay there rather than wander around throughout the year. In that case, why not build something more robust to live in? You'll need a number of houses, too. The people with you aren't strangers: they are your kin, so you're all content to live together.
No one is in charge; responsibilities are divided based on ability and typically without regard for gender. There is no wealth, no hierarchy. Tools are shared, skills are taught freely. Children observe domestic activities and learn from their parents and other kin. You may not hunt as much but you've begun keeping animals domestically, as beasts of burden and as food. Each family has their own milling stone for grinding flour to bake bread. A variety of crops are grown, almonds and barley and peas. Settled down with a stable food supply and the protection of your extended family, you can develop complex crafts, like pottery and obsidian tools. All of this, plus your food surplus, you can trade with other communities. They may be small villages or mobile bands. They see your city and shake their heads, wondering what you could be thinking with such a monstrous facility.
You care nothing for their ignorant taunts. You sit on your cow skin bed, wielding a brush similarly made with bovine hair, painting in ochre on the wall beside you. You imagine your city, layer upon layer, drawing the way it looks in your head. It's not a map, not really. It's fixing an idea, commemorating that you were here, that your people built this, and that you were happy.
The seasons wash over the city year after year. There are more people all the time--more children laughing and playing, and sometimes new people join, finally seeing the allure of your peculiar "city." But new ideas are also emerging. A friend's uncle has amassed a large store of grain and several milling stones, more than anyone else. No one stopped him from doing this as no one knew. He began to trade it for unusual goods: spices, animal skins not known to this region, pottery with strange designs, made of materials you could not imagine. He adorned himself in jewelry purchased with his excess goods--good that should have belonged to everyone, you think.
His brother was said to have confronted him, calling his behavior disgraceful, shameful, an insult to the gods. For effect, the offended brother smashed one of the goddess figures normally kept with the cereals. The man who had so much responded in turn with the cruelest punishment he could conceive: he had his brother's milling stone brought before him and shattered. "Now you can make no bread at all," he declared. "See what your jealousy has brought to you!"
No one knew what to do about this. No one had behaved this way before, not since before the city had been built, and that was long before you were born. It was not right, but your siblings and cousins gathered on the rooftop plaza to discuss the situation. You disliked gossip yet could not help but attend. They contemplated many options. One of the older men believed the best course was to send him away--to exile him. "If he wishes to behave like an animal, he may return to the animals!"
Some of the younger ones did not agree. "He has gained what he has gained by his own work. Should he not benefit from it?"
"Not to the detriment of all of us!"
"But we all have what we need, don't we? He has only take some of what we don't need, and has gotten things for himself that gave him pleasure."
"And what shall we do should all wish to live as he does?" the elder posed. "There is not enough food for all of us to trade it away as he has done. This was food we might need if the winter is too long and harsh, or should the next harvest fail. Perhaps he is ill with the spirit of greed. Perhaps he must ask the gods to cure him."
"There is nothing to cure," the youth protested. "He is a man seeking only what his heart desires. It is no more or less than any of us might like. Do the gods wish us to suffer, or for us to be happy?"
"The gods wish only our obedience, as you well know. They tell us their demands with the seasons and the omens. The gods have not given us ill signs nor should we tempt them. We should force him to go."
No matter what he's done, you think this is wrong. You add your voice to the forum. "We have never forced anyone to leave. We are kin, are we not? We are born together, grow up together, marry within the group, live and die together. We could no sooner force him away than cut off an arm."
"A gangrenous arm will kill you if not severed above the rot," the elder scolded. "That is old knowledge that you well know."
"He is not a limb, but a man," the other youth spoke up once again. "Do not compare him to lesser things. Take him as he is. Make him replace his brother's milling stone and apologize before the gods. That should pacify all parties."
"It does not solve the central problem," the elder went on. "If he does not alter his behavior, there will be more conflict. Together, we repel threats from without. We cannot stand against a threat from within. Do you all remember last autumn, when he was the play-god?"
"He enjoyed the part rather too much!" another elder noticed.
"Indeed, and soon he may see himself as a true-god. He would put himself above us, as he has put himself above his own brother. What shall he do, build atop our homes and claim it all as his own?"
"We are talking about things that have not happened," you stress to them. "We should have him apologize and replace the stone. That should be enough. If it is not enough, then we must speak of this again."
This did not satisfy anyone, but no one was willing to stand against it, and so it was proposed to the man who thought himself equal a god. His bitterness was evident, his disdain for his own brother shamefully displayed for all who witnessed. Through gritted teeth, he apologized. This was not sufficient, however: he needed to be loud enough for the gods to hear. So, he shouted it angrily. No one wished to argue that he had not completed this part of his obligation. It had all been stressful enough.
He gave his brother one of his several milling stones, though it was the one of lowest quality. It worked well enough but was smaller than the others, clearly a grudging fulfillment of the debt to his brother.
The brother accepted this without complaint. He, too, wished for the tension to abate.
The play-god remained angry, however. Not ten moons later, he threw his brother from atop the plaza. Two women witnessed who had no reason to lie. All of their close kin gathered to decide what to do, including you.
You could not argue with the proposed judgment: to do to him as he did to his brother. Kinslaying was a profound offense to the gods. The punishment was known only to tradition. It had not needed to be used in this place, ever. Now, it would see the blood of two men, spilled in violence in short succession. An ill omen to be sure, but how could kinslaying go unpunished?
He spat curses and obscenities as he was dragged by his arms to the edge of the roof plaza. He was allowed to wear his lavish accouterments, and he would not be robbed of them, even in death. He screamed as he was shoved over the edge. His blood stained the soil not far from the site of his brother's death. Justice was done; the gods, you all hoped, were placated.
But once killing had been invited to the city, like an unwanted guest it would forever refuse to leave.