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.

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.

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.

Today, we know that Sahara Desert as a vast sea of sand and salt flats. But up until around 5,000 years ago, this is how it looked.

It was a green landscape of Savannahs, lakes and rivers where early humans lived, hunted and fished.

(📷 flickr.com/photos/cchurch…) 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.

In 1982, a Turkish sponge diver Mehmed Mehmed Çakir was diving for sponges off the coast of Uluburun in southwestern Turkey.

He was about 44m deep when he came across a strange clutter of objects, half-buried in the silt & sand. He knew that he had discovered something ancient, and he quickly alerted archaeologists.

But he couldn't have guessed just how ancient these artefacts were, or how important they would prove to be.

A map showing the lands of the Maya at the height of their civilization, prior to the Classic Maya Collapse discussed in Episode 3. Here's a relief map so you can visualise the southern highlands vs. the northern lowlands.