On April 21, 1971, a little-known Maya manuscript — a calendar for calculating the cycles of Venus — went on view at the Grolier Club in Manhattan as part of an exhibition on Maya writing.

“Manuscript Could Change Views on Mayans’ Religion” announced a headline in The New York Times.

Michael Coe, a Yale professor of anthropology and an organizer of the exhibition, told the Times that the manuscript, which was owned by an anonymous private collector and had never before been on exhibit, was an “important find” that furnished new information on the importance of Venus to Maya religious beliefs and astrology.

“Only a half-dozen people know of the existence of this codex,” Coe told the Times.

The manuscript, if authentic, would be the oldest known book in the Americas and one of four surviving Maya codices. (The other three are located in Europe and named after the cities where they are housed: Dresden, Madrid, and Paris.)

Discovered by looters in a cave among a trove of Maya artifacts, the manuscript on view at the Grolier Club had not been subjected yet to scientific analysis, such as carbon dating, and Coe predicted that many of his fellow scholars would reject its authenticity. He was confident that the manuscript was genuine, saying he would “stake his professional reputation on it.”

Indeed, the 10-page manuscript on bark paper, which became known as the Grolier Codex, attracted many skeptics, including prominent scholars of Mesoamerica, but Coe never wavered in his belief in its authenticity.

More than 46 years after the Grolier Club show, Coe and three of his former students — Mary Miller, Sterling Professor of History of Art at Yale; Stephen Houston, the Dupee Family Professor of Social Science at Brown University; and Karl Taube, professor of anthropology at the University of California-Riverside — sifted through all known research on the 13th-century manuscript, including radio-carbon dating and other scientific analysis, and concluded that it is genuine. Their findings, published last fall in Maya Archaeology 3, a peer-reviewed volume, confirm that the Grolier Codex is the oldest known manuscript from the Americas and a unique window into Maya religious beliefs.

Their report made Discover Magazine’s top 100 science stories of 2016, landing at no. 64 on the list.

“We’ve answered all of the questions,” said Coe, the Charles J. MacCurdy Professor Emeritus of Anthropology. “The codex is real. No forger could have produced it.”

“This was no fake”

In the 1960s, Coe had heard rumors that Dr. Josué Sáenz, a wealthy Mexico City-based collector, had acquired a Maya codex.

“I was immediately suspicious,” Coe said.

Coe was in Mexico City during the summer of 1968 researching materials from an Olmec site he had spent three years excavating in southern Mexico. He was invited along with two colleagues — Gillett Griffin of Princeton University and Elizabeth Benson of Dumbarton Oaks Research Library and Collection — to have dinner with Sáenz at the collector’s house on Lomas de Chapultepec, overlooking the city.

“This guy had a magnificent house,” Coe said. “His dining room was lined with looted Maya stelae — huge stone sculptures largely from Guatemala. He was the number-one collector, at least in Mexico, of Pre-Columbian material.”

During dinner, Coe mentioned the rumor he had heard about the Maya codex. Sáenz acknowledged that he had acquired a manuscript, but admitted that an expert had advised him it was a fake, Coe said.

The Yale archaeologist asked to see the codex. Sáenz provided Coe with photographic prints of the codex. Each page featured a fearsome, warlike figure — a god — wielding a spear or other weapon. The pages also contained glyphs and “bar and dot” numeric symbols.

“I’ve seen a lot of fakes in my day,” said Coe, who frequently assisted the Internal Revenue Service in identifying forged Pre-Columbian artifacts. “I knew immediately that this was no fake.”

Coe brought the prints to New Haven where he shared them with Floyd Lounsbury, a Yale anthropologist and leading scholar of Maya hieroglyphs and culture, who agreed that the codex was a genuine Maya manuscript.

“We studied the living daylights out of it,” Coe said.

Lounsbury, who died in 1998, concluded that it was a calendar for calculating the course of Venus. He told Coe that half of it was missing — the complete calendar would have been at least 20 pages.

Coe was vacationing with his family in the southwest United States in 1970 when he encountered a couple of friends at the Kewa Pueblo outside of Santa Fe, New Mexico. His friends were members of the Grolier Club, a private society of bibliophiles, and they proposed hosting a show on Maya writing at the club.

“At this time, the Maya script was being broken, and we were just realizing that we could read it,” Coe said. “It was a very exciting time.”

Sáenz agreed to loan the codex to the Grolier Club for the exhibition, which lasted three months and drew widespread attention. Two years later, Coe published the codex in the catalogue for the Grolier Club exhibit. The debate over its authenticity revved into high gear.

Skeptics pounce

In 1973, Coe had radio carbon dating performed on sample from a disconnected page of the manuscript that had no painting on it. The test dated the bark paper to the 13th century. (The Mayans made their paper from fig bark.)

Following a brief period at Yale, during which Coe studied the manuscript with his students, the codex was taken to Manhattan and locked away in a bank vault. In 1977, it was returned to the in Mexico City and housed in a basement vault at the National Museum of Anthropology, where it remains today. It has not been on public display since the Grolier show.

J. Eric Thompson, a renowned Mesoamerican archaeologist, denounced the manuscript as a fake in 1975, shortly before his death. Thompson posited that large quantities of Pre-Columbian bark paper were available to forgers. He also pointed to differences between the Grolier Codex’s Venus calendar and a similar table found in the Dresden Codex, considered the masterpiece of the three Maya codices housed in Europe. He noted that ring numbers, numerical symbols, are used differently in the two codices.

Other critics have argued that red sketch lines visible on the codex’s paintings suggest the kind of sloppiness one would expect in a forgery. Still others pointed to sharp cuts in the bark paper where pages join as the mark of a faker.

The codex’s murky provenance — discovered by looters, not archaeologists, in a cave likely somewhere in southwestern Mexico — also fueled doubts. (The cave’s precise location is unknown, Coe said.) Sáenz purchased the manuscript and a half-dozen other pieces found in the same cave, including a turquoise-encrusted wood mask and a sacrificial knife, directly from the looters. As the story goes, Sáenz was taken in a small plane to a remote airstrip. As a precaution, he was blocked from looking at the plane’s compass to make it difficult to determine the airfield’s location.

Some of the skepticism was fueled by politics, said Mary Miller, the former dean of Yale College and distinguished art historian.

Sáenz played a prominent role in organizing the 1968 Summer Olympics in Mexico City. Many Mexicans objected to the enormous expense of hosting the games, believing public money would be better spent on social services. During a mass protest in the city’s Tlatelolco Plaza 10 days before the games, police and military shot into the crowd, possibly killing hundreds of civilians.

“Sáenz was a controversial figure,” she said. “People disliked his involvement with the 1968 Olympics. People resented the fact that he was a private collector who didn’t donate his collection to the nation. They disliked the man and his collection, and they wanted to treat everything in it as fake.”

“Get the band back together”

As years passed and doubts about the codex endured, Coe developed the urge to answer the skeptics once and for all.

“It was time to put this thing to rest,” he said.

He first turned to Miller, an authority on Mesoamerican art whom he had taught while she was a Yale graduate student.

“I knew I needed Mary on my side,” he said.

Coe also enlisted the help of Houston, a leading expert on Maya hieroglyphic writing, and Taube, who is internationally recognized as the top authority on Mesoamerican iconography. Both are former graduate students of Coe’s.

“Mike had come to feel as though this manuscript that he had been the first to publish had gotten a bad rap,” said Miller, who directs the Institute for the Preservation of Cultural Heritage at Yale’s West Campus. “He wanted to get the band back together in order to do justice to it.”

The team sought to address all doubts regarding the manuscript’s authenticity. They examined its physical structure, style, and content. They describe the scientific analysis the manuscript has undergone over the years, including a second round of radiocarbon testing on the manuscript’s paper, which also provided an approximate date in the 13th century.

“It’s pretty clear that the paper was made from fig bark that lived between 1220 and 1240,” Miller said.

In 2007, scientists in Mexico determined through non-invasive methods that the manuscript’s pigments and inks contained no modern materials and that their composition was consistent with the pigments used in the three Maya codices in Europe.

The scientists also determined that blue pigment found on page 10 is composed of indigo dye and palygorskite, a clay mineral the Mayans used to make blue pigment. The mineral was not identified as a component of Maya blue until 1964, and it was not synthesized in a lab until the 1980s.

“You couldn’t have made this pigment in the 1960s,” Miller said.

As to the presence of the red sketch lines, Coe’s team showed that Maya artists often sketched their paintings in this manner and on occasion they deviated from sketch lines.

“It’s not a reason to think that this is a fake,” Miller said. “The artist who painted this wasn’t concerned about the sketch lines. He probably wasn’t a very sophisticated artist, but he knew what he was doing.”

The sharp-edged holes in the manuscript are consistent with natural erosion of the plaster of Paris that coats the codex’s pages, according to Coe’s team.

“The looters who found this may have cleaned it up a bit before presenting it to the collector, but modern cutting does not affect its authenticity,” Miller said.

They show, contrary to Thompson’s critique, that difference in the use of ring numbers between the Dresden and Grolier codices is not evidence of a forgery, but an indication that ring numbers were used in different ways. In 2012, archaeologists uncovered a painted wall in Guatemala that shows a variety of methods for using ring numbers.

“This was manna from heaven for us,” Miller said.

The codex’s iconography contains details that a forger in the 1960s could not have known about, according to the team’s report.

For example, a mountain god pictured on the manuscript’s ninth page has a cleft at the center of his head that flares out in both directions. The cleft appears to contain maize kernels. A similar image was discovered in a wall painting in 1974. Forgers in the 1960s would have required foreknowledge of this discovery, Coe’s team argues.

Scholars have argued that the Grolier Codex mistakenly depicts all cycles of Venus as dangerous, asserting that the Maya only considered Venus dangerous when it appeared as the Morning Star. Coe’s team demonstrates that the planet was considered dangerous during its entire 584-day cycle.

“A reasoned weighing of the evidence leaves only one possible conclusion: Four intact Maya codices survive from the Pre-Columbian period, and one of them is Grolier,” they write.

A dangerous planet

According to Coe, there are two reasons why so few Maya codices survive: First, the 13th century was a period when Maya civilization endured widespread drought, declining population, and social and political strife. Books and libraries likely were lost amid the turmoil, Coe said. Then the Spanish destroyed hundreds of codices, assuming that they were idolatrous, in an effort to repress Maya language and culture.

As Coe explained to the Times in 1971, the manuscript offers insight into the role of Venus in Maya religion and astrology.

“Venus was considered an extremely dangerous planet, and you wanted to stay out if its rays,” Miller said.

The deities depicted on the codex’s pages, including death and serpent gods, are an intimidating lot. Some hold prisoners. The skeletal death god on the sixth page is decapitating a captive with a sacrificial blade. A flint blade protrudes from the deity’s nasal cavity. Blood spills from the captive’s neck.

While the Dresden Codex is considered a masterwork, the Grolier Codex is a modest, workaday object likely created by a provincial artist, Miller said. It features characteristics of art and writing from the highlands of Central Mexico.

Both Coe and Miller relished the experience of working together with longtime colleagues.

“The work took us about two years,” Coe said. “The four of us made a wonderful team.”

For Miller, Houston, and Taube, it was an opportunity to pay tribute to a mentor.

“We all had fantastic opportunities and Mike has been instrumental to our success,” Miller said.