This era is known as the African Humid Period, and it peaked between 9,000 and 6,000 years ago.
In those days, the landscape of the Sahara would have supported rolling grasslands, lakes and rivers, as well as sparse forests of trees like acacia.
It was also home to Neolithic human communities.
In fact, rock paintings have been found in the central Sahara that depict abundant animal life, and even people swimming, in places that are today a barren desert.
(📷 Dr. Stefan Kröpelin, Köln University)
These communities were largely hunter-gatherers, but were increasingly beginning to practise pastoralism, ie. keeping cows and sheep.
They observed the world around them, and created incredible artworks like the so-called Dobous Giraffes (pictured).
But the days of their societies were numbered.
Changes in the earth's orbit known as its orbital precession, a change in tilt that cycles every 25,000 years, forced the African monsoon rains southward, and the Sahara became drier.
Trees and large plants would have died first, until only grass remained. And then even the grass would have withered and died.
Without roots to hold together the earth, the topsoil blew away, and desertification set in.
While estimates vary wildly, some believe that this process could have taken only a few hundred years.
Human societies fled the advance of the desert, moving to the coasts. Their populations concentrated there, and they built settled societies that lived in cities.
The Green Sahara reminds us of the dramatic changes that can arise from even gradual planetary shifts.
It reminds us that history is a record of change, and that things we often take for granted are not as certain as we might think.
I talk more about the Green Sahara and its legacy in the latest episode of Fall of Civilizations.
Find it here, or on any major podcasting platform:
It's often said that the indigenous people of South America never developed a system of writing.
But this isn't entirely true. In fact, they created a unique and complex system of notation based on the tying of knots, known as quipu, which remain undeciphered to this day.
The quipu were usually made from string, spun from cotton fibers, or the fleece of camelid animals like the alpaca and llama.
The cords stored information with knots tied in vast assemblages of string, sometimes containing thousands of threads.
In some analysed quipu, the combinations of thread length, colour, knot type and knot position allow for up to 95 possible combinations, which could represent numbers, symbols or even sounds.
One of the most remarkable journeys to take place in the ancient world was that of the Chinese explorer Gan Ying.
In the first century, he became the first recorded human to travel the whole length of the route known as the Silk Road, and wrote a remarkable account of his trip.
For the Han dynasty of ancient China, the first century was a time of unprecedented contact with the rest of the world.
They had succeeded in re-conquering a fractious desert region to the West known as the Tarim basin, a sandy depression in the heart of the Tibetan Plateau.
The Tarim basin is home to the Taklamakan Desert, the second largest shifting sands desert in the world.
This desert is the only route to the West in the north of China, and so for millennia trade caravans of Bactrian camels have passed through the oasis cities of this region.
A thread on some of the most amazing examples of art in the Aztec codices.
These were illustrated books written by the indigenous people of Mexico both before and after contact with Europeans, and contain incredible glimpses into their lives, their memories, and their beliefs.
The Aztec codices were books written on deer skin or bark paper. The Aztecs had vast libraries, but after the Spanish conquest of the city of Tenochtitlan in 1521, all of these libraries were destroyed.
Only 16 pre-contact codices have survived.
Folio 65r of the Codex Mendoza, an Aztec codex from c.1541.
This page shows how an Aztec warrior and an Aztec priest could rise through the ranks of their orders. The rank of a warrior depended on how many enemies he had captured during war.