"We have found the stairs of this, much older pyramid. The timeline is going to need to be revised," said Patricia Ledesma, one of the archaeologists excavating the site.

The ruins are 36 feet high and were found in the central Tlatelolco area -- once a major religious and political centre for the Aztecs.

Historians previously thought that Tlatelolco was founded by the Aztecs in 1325, at the same time as the nearby twin city of Tenochtitlan.

Tenochtitlan was razed by the Spanish in 1521 to found Mexico City as we know it, signifying the total conquest of the Aztecs.

But Mexico City still has many ruins from the time before the Conquistadors.

Archeologists recently unearthed what could be the main pyramid of Tenochtitlan.

The newly discovered pyramid in Tlatelolco could have been built as early as 1100 or 1200, meaning that the Aztecs developed their civilisation earlier than was previously thought.

The dig has also found a sculpture that could either be the Aztec rain god Tlaloc or the god of the sky and earth Tezcatlipoca.

Archaeologists have also founf five skulls and a series of rooms near the ruins that may date from 1431.

"What we hope to find soon should tell us much more about the society of Tlatelolco," said Ledesma.