Barbara Williams of the University of Wisconsin-Rock County and Maria del Carmen Jorge y Jorge of the Universidad Nacional Autonoma de Mexico studied the maps used by the Acolhua people of Tepetlaoztoc to document agricultural properties.

"What we found that was surprising, was how accurate the Aztec surveyors were from a mathematical perspective," said Williams.

"What we thought we knew about the Aztec measuring system was a little simplistic."

"We've determined that it was more complex."

"They used the four mathematical operations of addition, subtraction, multiplication and division."

"But in almost all of the early societies, they could do everything they needed to do, with just those four."

"They didn't need square roots."

"They didn't need trigonometry."

The researchers used trial and error methods to decode the meanings of various symbols that turned out to describe fractional areas on the maps.

"We found these smaller units of measure that we call monads that have the role of a fraction," said Dr Jorge y Jorge.

"We don't like to call them fractions, though, because they were considered as unitary entities like inches, seconds or minutes."

Scientists discovered nearly in 1980 that the Aztecs could calculate areas, but the method was largely unknown until now.

"This increases our understanding of Aztec culture," said Williams.

"It gets to the idea that it was a numerate society in the rural areas as well as the urban areas -- among the surveyors as well as the priests and the royalty."