Symbols like hearts and arrows were used to calculate fractions
Researchers in Mexico and the US claim to have cracked the meaning of mysterious ancient symbols on 16th-Century Aztec documents.
A study in the journal Science claims the symbols, like hearts and arrows, represent mathematical fractions.
The patterns are the first evidence of fractions being used in indigenous counting systems in the Americas.
The documents belonged to an Aztec community in dispute with their Spanish ruler over taxes.
Mapped out on the manuscripts are farmers' fields with length and width measurements and even areas annotated with lines and dots.
Up until now no-one has been able to make sense of how the linear measurements and the areas of the fields added up.
But Maria del Carmen Jorge y Jorge, of Mexico's National University, says she has cracked the code.
As well as the lines and dots, there are other mysterious symbols - such as arrows, arms and hearts, she says.
These represent fractions, she explains, and when you add them into the calculations, the Aztecs' sums all make sense.
But the similarities with modern mathematics end here - like other historic communities of the world, the Aztecs counted whole numbers in 20s, using their fingers and even their toes if necessary.