The city, which contains flat-topped pyramids, was in use between roughly 600 B.C. and 300 B.C., a time when the first cities were being constructed in the area. No other city from the Maya world was planned using this grid design, researchers say. This city was "organized in a way we haven't seen in other places," said Timothy Pugh, a professor at Queens College in New York.

"It's a top-down organization," Pugh said. "Some sort of really, really, powerful ruler had to put this together."

The ancient Mexican city of Teotihuacan also used a grid system. But that city is not considered to be Mayan, and so far archaeologists have found no connections between it and the one at Nixtun-Ch'ich', Pugh said. [In Photos: Mayan Art Discovered in Guatemala]