No human so far in our story has, as far as we know, ever claimed to be a god. Holy men of the hunter-gathering people's caves venerated the spirits and the gods of the Earth, sky, beasts and woods, but there is no suggestion that they ever thought that they themselves were part of divinity. Rather, these ancient people were so in awe of the gods that they sensed their presence all around, from the pinpricks in the tin roof of the heavens to the awesome forces of floods, thunder, lightning, sunshine, moon, rivers, woods and war.

So, to make the leap from seeing the gods as otherworldly to regarding them as real, living, breathing, walking and talking humans is a big one. What power and magnificence would be bestowed on the person who managed to convince others that he was a god on Earth!

According to one early civilisation a member of Homo sapiens could indeed be a living god, possessing that most precious gift so fruitlessly craved by King Gilgamesh: divine immortality. They called him Pharaoh. He ruled a stretch of North Africa we now call Egypt through a succession of more than 30 dynasties, lasting 3,000 years.

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Pharaoh was all-powerful. His people created for him extraordinary monumental buildings in the forms of palaces, temples and tombs. The only survivor of the famous Seven Wonders of the Ancient World is the Great Pyramid of Giza, built as a tomb for one of the earliest pharaohs, called Khufu (known as "Cheops" in Greek), who died in 2566BCE.

This monumental construction originally towered skywards a massive 147m – that's over 50m taller than Big Ben. It still contains more than 2 million blocks of stone, each one weighing more than a pick-up truck.

Hundreds of thousands of people worked to build structures like this. Modern experts are still at a loss to explain how the ancient Egyptians could have cut, transported and hauled into place so many huge blocks of stone, pushing them upwards into the sky from the flat, sandy desert in defiance of everything natural around.

The Egyptians were the first example of a human civilisation whose rulers amassed extremes of wealth and absolute power over men. Their unprecedented riches and glory were underpinned by a belief that when they left this world they would join the gods in heaven for all eternity. Those who curried sufficient favour could be taken along too, if Pharaoh so chose, entering into a blissful life amongst the reeds of everlasting peace.

From about 6,000 years ago nature gave these aspiring all-powerful human rulers a big helping hand in the form of a river and some strategic changes in the climate. Together they transformed the north-eastern tip of Africa into one of the most fertile and best protected lands on Earth.

Unlike the rivers of Mesopotamia, the Nile naturally floods once a year, bringing with it a supply of fresh, nutrient-rich soil, earth and sediment – perfect for growing crops.

With a natural supply of nutrients and a fresh deluge of rainwater each year, there was no risk of salt poisoning here. Following the end of the Ice Age 11,000 years ago, North Africa was a verdant land of rolling grasslands dotted with trees and vegetation.

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Over the years, hunter-gathering tribes established themselves near the Nile, settling into small villages and communities. They learned to domesticate the wild cattle, goats and sheep that grazed the savannah, providing them with plentiful supplies of milk, wool and leather. Over time, knowledge about farming crops such as wheat, barley, grapes and flax had reached them via nomadic traders from Mesopotamia and across the land from people like the Natufians (see Part 5). These river-dwellers were now ideally placed to grow into a rich and powerful civilisation.

They also had another advantage. From about 6,000 years ago the land around the upper Nile began to dry out – partly as a result of cyclical changes in the Earth's axis that re-directed rainfall patterns and partly because new human activities such as growing crops and herding animals reduced natural water levels. By 4,000 years ago what was once a landscape full of crocodiles and hippos wallowing in plentiful streams of water had become the arid land we know today as the Sahara Desert.

The encroaching desert was good news for these people because it provided them with an almost impenetrable barrier to invaders. There was no need for defensive city walls, towers, castles or elaborate military installations here. From about 2000BCE the only way other people could disrupt the ancient Egyptians' way of life was either to cross hundreds of miles of barren desert or to come by sea, which was an equally daunting challenge due to a natural defence shield in the form of the boggy, reedy marshlands of the lower Nile delta.

Thanks to these natural barriers, the Egyptian people lived in relative peace and security for much of their history, able to develop their own way of life with little outside interruption.

The Nile brought another gift, too – one which helps explain why it was here that such powerful rulers were able to rise up and take for themselves the title of god. The river provided a two-way causeway that allowed easy passage up and down the country. The current arrangement of the Earth's tectonic plates means that the prevailing winds across Egypt blow north to south – in the opposite direction to that in which the river flows. A vessel could simply float downstream, then raise a sail for the return journey. What could be better for controlling a kingdom than a well-protected, fertile valley with an easy-to-navigate, two-way river system?

Nowhere on Earth had as many helpful natural ingredients to aid the growth of an advanced human civilisation as did ancient Egypt 5,000 years ago.