1 . The Mysteries of The Maya

Extending south from parts known as Mexico into Central America,     1    .The Maya built impressive palaces and temples and step pyramids. How were they built without the use of wheels, metal tools or even animal power?     2     They applied this understanding to the Maya calendar, which was accurate to within 30 seconds per year.

The fact that Maya society was technologically primitive makes its achievements all the more incredible and mysterious.     3     By 700 AD, Maya civilization was at its peak. Yet, within just a couple of generations, it began to mysteriously decline. The cities were left to be taken back by the jungle.

Why Maya civilization collapsed remains a mystery. A deadly disease? Conflicts between cities?     4     They had turned wetlands into fields for growing grains, and had dug huge canal systems. As their population expanded, yet more land was needed for agriculture and more trees for construction. By changing the landscape in this way, the Maya people unknowingly reduced their ability to deal with natural disasters.

    5     Some recent studies have found that there were far fewer tropical cyclones (热带气旋) than usual between 700 AD and 1000 AD, which is likely to have led to a series of droughts. These droughts would have led to food shortages, conflicts and ultimately, the downfall of the cities.

Whatever the reasons, Maya civilization largely disappeared within the deep jungle. Its once-great cities fell into ruin, leaving various mysteries for later people to solve.