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We next headed north to Tikal -- one of the most powerful kingdoms of the ancient Maya. It reached its apogee during the Classic Period -- 200 to 900 AD. But Tikal's heyday ended abruptly at the end of the 10th century AD. The city was abandoned and soon enveloped by jungle.

Exactly why that happened remains a mystery. Was it due to an attack by the great metropolis to the north, Teotihuacan, in the distant valley of Mexico? Some historians believe overpopulation and deforestation led to crop failure, and people chose to abandon the city rather than starve.

Tikal was "rediscovered" in 1848. Today, Tikal National Park, a UNESCO World Heritage site, encompasses 575 square kilometres of jungle and thousands of ruined structures, many of which are still being excavated.