MEXICO CITY — Fifty-four years after it was sold by looters, an ancient Maya pictographic text was judged authentic by scholars Thursday.

Mexico’s National Institute of History and Anthropology said the calendar-style text was made between 1021 and 1154 A.D. and is the oldest known pre-Hispanic document.

The 10 surviving pages of the tree-bark folding “book” will now be known as the Mexico Maya Codex. It had been known as the Grolier Codex. It may have originally had 20 pages, but some were lost after centuries in a cave in southern Chiapas state.

It contains a series of observations and predictions related to the astral movement of Venus. Mayan texts are written in a series of syllabic glyphs, in which a stylized painted figure often stands for a syllable.

This undated photo released by Mexico's National Anthropology and History Institute (INAH) shows a worker inspecting an ancient Maya pictographic text in Mexico City. INAH via AP

A Mexican collector bought it in 1964, and it was first exhibited at the Grolier Club in New York in 1971.

Collector Josue Saenz returned the book to Mexican authorities in 1974.

The fact that it was looted and had a simpler design than other surviving texts had led some to doubt its authenticity.

“Its style differs from other Maya codex that are known and proven authentic,” the institute said in a statement. About three other later Maya “books” survived an attempt by Spanish conquerors to destroy Mayan artifacts in the 1500s.

But the institute said Thursday that because the book was written so early, it had been created in an era of relative poverty compared to the other works. It said a series of chemical tests proved the authenticity of the pages and the pre-Hispanic inks used to write it.

While previous studies had supported the authenticity of the text, it was the end of decades of doubts for the book.

“For a long time, critics of the codex said the style wasn’t Mayan and that it was ‘the ugliest’ of them in terms of figures and color,” said institute researcher Sofia Martinez del Campo. “But the austerity of the work is explained by its epoch, when things are scarce one uses what one has at hand.”

FOLLOW NBC LATINO ON FACEBOOK, TWITTER AND INSTAGRAM.