Since it was reportedly unearthed in the 1960s, the 13th century Grolier Codex – one of the rarest books in the world – has been regarded with scepticism.

Some people have questioned the authenticity of the book, suggesting that it was forged by modern writers.

However, a new study has reviewed all known research on the manuscript, and suggests that the Grolier Codex is both genuine, and likely the oldest of all surviving manuscripts from ancient America.

Since it was reportedly unearthed in the 1960s, The Grolier Codex – one of the rarest books in the world – has been regarded with scepticism

THE GROLIER CODEX The Grolier Codex was discovered in 1965 by Josué Sáenz in a cave in in the highlands of Chiapas near Tortuguero, Mexico and is thought to date back to around 1230. The book consists of 10 painted pages decorated with ritual Mayan iconography and a calendar that charts the movement of the planet Venus. The Venus calendars counted the number of days that lapsed between one rising of Venus and the next, or days when Venus, the morning star, appeared in the sky before the sun rose. This was important because measuring the planet's cycles could help Mayan people create ritual cycles based on astronomical phenomena. According to the researchers, the book is not markedly beautiful, and is more focused on images than being literate. Advertisement

The book consists of 10 painted pages decorated with ritual Mayan iconography and a calendar that charts the movement of the planet Venus.

Researchers from Brown University in Rhode Island looked at previous studies on the document, analysing it 'without regard to the politics, academic and otherwise that have enveloped the Grolier', according to the study.

Stephen Houston, Professor of Social Science at Brown University, who led the study, said that the research is 'a confirmation that the manuscript, counter to some claims is quite real.

The Grolier Codex was found by Josué Sáenz in a cave in Mexico in 1965, before it was sent to New York and displayed at the Grolier Club, the private society of bibliophiles that gives the codex its name.

For years, people have argued about the legitimacy of the book, suggesting that modern forgers had enough knowledge of Mayan writing to create a fake codex.

The book was found in a cave along with six other items, including a small wooden mask and knife, which some critics have said were fake.

However, in recent years, the items have been proven to be authentic.

Other sceptics ridiculed Mr Sáenz's account of finding the book after being tipped off by two looters.

Mr Houston said: 'It became a kind of dogma that this was a fake.

'We decided to return and look at it very carefully, to check criticisms one at a time.

The Grolier Codex was discovered in 1965 by Josué Sáenz in a cave in in the highlands of Chiapas near Tortuguero, Mexico and is thought to date back to around 1230 BC

The book consists of 10 painted pages decorated with ritual Maya iconography and a calendar that charts the movement of the planet Venus

THE ANCIENT MAYA AND THE STARS Mayan civilisation thrived for more than 2,000 years with its heyday being 300 to 900 AD. During that time, the ancient people built incredible cities using advanced machinery and gained an understanding of astronomy, as well as developing advanced agricultural methods and accurate calendars. The Maya believed the cosmos shaped their everyday lives and they used astrological cycles to tell when to plant crops and set their calendars. It's therefore likely the Maya may have chosen to locate their cities in line with the stars. It's already known that the pyramid at Chichén Itzá was built according to the sun's location during the spring and autumn equinoxes. When the sun sets on these two days, the pyramid casts a shadow on itself that aligns with a carving of the head of the Mayan serpent god. The shadow makes the serpent's body so that as the sun sets, the terrifying god appears to slide towards the earth. Source: History.com Advertisement

'Now we are issuing a definitive [reproduction] of the book. There can't be the slightest doubt that the Grolier is genuine.'

The researchers analysed the 50-page book, looking at the origins of the manuscript, the nature of its style, and how it was created.

Analysis of the composition, including thin red sketch lines and blue pigments strongly suggested that The Grolier was in fact authentic.