Since the mid-20th century, archaeologists have discovered hundreds of Dead Sea Scrolls amid the rocky hills of Qumran, an archaeological site in the Judaean Desert of the West Bank. Scholars have deciphered most of these ancient texts, but a few exist in dozens of tiny fragments, making them difficult to piece together. After a year of painstaking work, however, researchers at the University of Haifa have assembled one of the last un-decoded scrolls. Intriguingly, according to Daniel K. Eisenbud of the Jerusalem Post, the text offers new insights into the unique calendar that was used by the mysterious people who penned the scrolls.

A previous investigation into the 60 fragments that make up the new scroll had concluded that the pieces came from different texts. But when Eshbal Ratson and Jonathan Ben-Dov of the University of Haifa’s Department of Bible Studies took a second look, they found that the fragments actually came from a single text. This leaves only one Dead Sea Scroll that has yet to be deciphered.

The scrolls, which date from the 3rd century B.C. to the 1st century C.E., consist of a mixture of Biblical manuscripts and other religious writings. Many scholars believe that the scrolls were produced by an ascetic group known as the Essenes, who withdrew to a hermetic lifestyle in protest over the way the Second Temple in Jerusalem was being run. That attribution, however, is not universally accepted.

Like a small number of other Dead Sea Scrolls, the newly deciphered relic was written in code—not because it contained sensitive information, but because using a secret script allowed the sect’s leaders to display rarified knowledge, according to a University of Haifa press release. But the person who wrote the text, which is concerned with the Qumran group’s unusual calendar, appears to have made several errors: a second scribe added details about missing dates in the margins between the text’s columns.

The mainstream lunar Jewish calendar, which is still in use today, relied heavily on human observations of moon to make determinations about when the new month began. “By contrast, the 364-day calendar was perfect,” Ratson and Ben-Dov say in the press release. “Because this number can be divided into four and seven, special occasions always fall on the same day. This avoids the need to decide, for example, what happens when a particular occasion falls on the Sabbath, as often happens in the lunar calendar.”

As they patched together the pieces of the manuscript, Ratson and Ben-Dov discovered that the text mentions two special occasions that are attested to in other Dead Sea Scrolls, but are not mentioned in the Bible: the festivals of the New Wine and the festival of the New Oil. These events were extensions of Shavuot, a holiday that marked the harvest of new wheat. According to the calendar laid out in the scroll, Shavuot fell 50 days after the first Sabbath following Passover; the festival of New Wine came 50 days later, and the festival of New Oil came 50 days after that.

The researchers were also excited to discover the name of four “special days” that marked the transition between seasons. These days are mentioned in other scrolls, but the new text specifies that they were called “tekufah,” a word that means “period” in modern-day Hebrew.