Tikal is an ancient Mayan site in northern Guatemala that has been partially reclaimed from the jungle. The site was active between 200 and 850 A.D. Most of the larger temples were constructed in the eight century AD when the Mayan civilization was at its peak in Tikal. Tikal declined during the ninth century AD and was subsequently abandoned and lost to the jungle.
The Tikal National Park website has a very good historical write-up and some interesting pictures.