The miracle of Jewish history is that we have been able to survive as one nation for millennia. Despite being scattered throughout the world, immersed in different cultures, and speaking different languages, Jews everywhere read the same Torah and celebrate the same holidays. One of the factors that unite us is the Jewish calendar; we all eat matzah on the same Seder night and fast on the same day of Yom Kippur.

Our Sages understood that maintaining the Jewish calendar was crucial to Judaism’s survival. They went to great lengths, at times risking their lives, to continue the practices required to preserve the calendar. There were two components to maintaining the calendar: sanctifying the months and adding leap years when necessary. The former ensured consistency with the lunar cycle while the latter ensured consistency with the solar cycle, guaranteeing that Passover always occurs in the spring, as the Torah commands.

After the Destruction of the Second Temple

While the Second Temple stood, maintaining the Jewish calendar was the job of the Sanhedrin, the Jewish Supreme Court located in one of the Temple’s chambers. After the Romans destroyed the Temple, the surviving members of the Sanhedrin moved to Yavneh, a town to the west of Jerusalem, close to the Mediterranean Sea.

According to Roman law, a province that rebelled against Roman rule and was defeated lost all political powers and rights. Thus, the surviving Jewish community in Judea was not allowed to have its own governing body, such as a Sanhedrin. For several years after the destruction, all decisions affecting Jewish life were made by individual sages.1 While history does not preserve much information about life in Yavneh shortly after the Temple’s destruction, presumably the calendar was maintained privately, out of sight of the Romans.

A few years later, once the Roman wrath had cooled off, the Sanhedrin reconvened in Yavneh and resumed the work of maintaining the calendar. Due to Roman suspicion and persecution, the Sanhedrin and its sages had to move from place to place, but continued to sanctify the months and add leap years, sometimes clandestinely. The Talmud tells us that Rabban Gamliel, the head of the Sanhedrin, once declared a leap year in an attic,2 while the great sage Rabbi Akiva, already advanced in years, had to travel to Nehardea in Babylonia in order to declare a leap year.3

Under Emperor Hadrian

The task became harder after the Bar Kochba revolt during the reign of the Roman Emperor Hadrian, about half a century after the destruction of the Second Temple. When the Romans suppressed the revolt, they slaughtered hundreds of thousands of Jews and razed Jewish towns and villages to the ground. Realizing that the Jewish people’s strength lay in Torah learning and observance, Emperor Hadrian enacted severe decrees against teaching and observing the Torah.

Shortly after the failed revolt, in 133 CE, the Romans arrested Rabbi Akiva for teaching Torah in public. While in jail awaiting his execution, Rabbi Akiva’s concerns lay with the future of the Jewish people, including the continuity of the calendar. From his jail cell, Rabbi Akiva determined three consecutive leap years, ensuring Jewish continuity for the near future.4

Semicha, at Great Cost

But the long-term future was still uncertain. The sages had to ensure that the calendar would be maintained in the next generation, and that involved a complication. Only rabbis who had received semicha—genuine rabbinical ordination—had the authority to add leap years to the Jewish calendar.

The institution of semicha was an important part of Jewish life in its own right. Semicha authorized rabbis to rule on the laws of fines, punishments, and other complicated matters. Maintaining the calendar was one of many of the semicha bearers’ responsibilities.

Semicha could be granted only by someone who had received semicha himself, thus forming an unbroken chain from Moses to Joshua and on (due to the challenges discussed in this article, semicha has long ceased to exist in our times).

The problem was that Emperor Hadrian had forbidden the granting of semicha under the threat of death—not only to the ones giving or receiving semicha, but to all the residents of the town where such a ceremony would take place. And given that the Romans had already razed a number of Jewish towns to the ground, this threat was not to be taken lightly.

After the Romans cruelly executed Rabbi Akiva, few rabbis were left who had received semicha and had the ability to pass it along. Among them was the elderly Rabbi Yehuda ben Bava, who was determined to preserve the institution of semicha for future generations.

Rabbi Yehuda ben Bava was willing to risk his own life but not the lives of others. Therefore, he chose a location far from any inhabited area, between two large mountains in the north of Israel. There, he gathered the five main students of Rabbi Akiva: Rabbi Meir, Rabbi Yehuda, Rabbi Shimon, Rabbi Yosei, and Rabbi Elazar ben Shamua. (Some say there was a sixth, Rabbi Nechemia.)

Rabbi Yehuda ben Bava granted semicha to each of the aspiring rabbis. Unfortunately, the Romans discovered them and realized what had just taken place.

“My sons, run!” cried Rabbi Yehuda ben Bava.

They asked, “Our teacher, what will become of you?”

Weak in body but strong in spirit, Rabbi Yehuda ben Bava replied, “I will stay here like a rock that cannot be overturned.”

The Roman soldiers threw 300 spears at the elderly rabbi, but he refused to budge. By the time the Romans managed to move his lifeless body and get through the narrow mountain passage, all the newly ordained rabbis were long gone.5

The New Rabbis Continue the Calendar

The rabbis ordained with such self-sacrifice by Rabbi Yehuda ben Bava escaped to Babylonia. There, they continued learning and teaching Torah until some time after Emperor Hadrian’s death, when it was deemed safe for them to return to the Land of Israel.

Upon their return, c. 142 CE, they had much work to do to revive the broken spirit of the persecuted Jewish people. Among their tasks was ensuring the continuity of the Jewish calendar, and they gathered in the Valley of Rimon to proclaim a leap year.6

Tragedy in Lod

According to the Talmud, the preferred location for proclaiming a leap year is Judea, in the center of the Land of Israel.7 In times of danger and persecution, however, leap years have been proclaimed in any location deemed safe, including in the Diaspora.

Towards the end of the 2nd century CE, the Roman persecution subsided. The head of the Sanhedrin, Rabbi Judah the Prince, maintained friendly relationships with the Roman rulers. The Sanhedrin at the time was located in the north of Israel, where it had moved back in the days of Emperor Hadrian.

In 193 CE, Rabbi Judah the Prince decided that it was safe to proclaim the upcoming leap year in Judea. He sent a large delegation (24 wagonloads) of rabbis to the Judean town of Lod. The Talmud tells us, “The evil eye entered them, and they all died at once.”8 9

After this tragedy, the decision was made to proclaim leap years in the Galilee, in the north, rather than in Judea.

Perilous Missions

For another century, the heads of the Sanhedrin quietly maintained the calendar. The Roman rulers had no great love for the Sanhedrin, but as long as the Jews paid their taxes they did not interfere with its work.

The Jewish community’s situation took a turn for the worse when Roman Emperor Constantine converted to Christianity early in the 4th century CE and encouraged the spread of Christianity throughout his Empire. He embarked on a number of great building projects in the Holy Land but also enacted several anti-Jewish laws and made life difficult for the dwindling Jewish communities there.

By that time, due to persecution, a significant percentage of Jews had moved into the Diaspora, mostly to Babylonia. The problem arose of how to inform the distant Babylonian Jews of the Sanhedrin’s decisions in a climate antagonistic to the Sanhedrin and the Jewish community in general.

The messengers dispatched from the Land of Israel to Babylonia faced great danger. They could be arrested or even executed. The sages sent coded messages to protect both the integrity of the calendar and the messengers themselves.

The Talmud brings an example of a coded message sent to Rava, one of the Babylonian sages:

A pair came from Rakkath. They were captured by an eagle. In their possession are items made in Luz. And what are they? Blue cloth. In the merit of [Divine] mercy and their own merits, they emerged in peace. And the offspring of Nachshon sought to establish a pillar, but the Edomite did not allow them. Nevertheless, the masters of gatherings gathered and established a pillar in the month in which Aaron the Priest died.10

In this message, Rakkath is another name for Tiberias, where the Sanhedrin was located at the time. The eagle refers to the Roman powers, whose emblem included an eagle. Thus despite traveling with cloth and posing as regular merchants, the messengers were captured by the Romans (but were later released, presumably due to lack of any incriminating evidence).

Nachshon was the first head of the tribe of Judah. Here, “the offspring of Nachshon” refers to the head of the Sanhedrin. “Pillar” is the code word for “month,” and “masters of gatherings” refers to the Sanhedrin. Aaron the Priest died in the fifth month (Av). Thus, the message to the Babylonian Jewry means that in the month of Av, the Sanhedrin had decided to proclaim the next year a leap year.11

Despite the danger and the obstacles, it seems from the Talmud that the Babylonian Jews received the message and were able to maintain the same calendar as the Jews in the Holy Land.

The Calendar of Hillel II

The increasing Christian persecution forced more and more Jews to leave the Land of Israel. By the mid-4th century CE, all the major centers of Jewish learning in the Holy Land had been either destroyed or relocated to Babylonia. This posed a threat to the institution of semicha, as well as to the continuity of the Jewish calendar.

In 359 CE, the head of the Sanhedrin, Hillel II, came to a decision that would forever change Jewish history and practice.12 Because semicha could only be granted in Israel, Hillel II realized that, sadly, the institution of semicha was coming to an end. There was nothing he or anyone else could do to salvage it. He could, however, do something to salvage the institution of the Jewish calendar.

As the leader of the tiny remaining Jewish community in the Holy Land, Hillel II convened a court. Based on their extensive knowledge of astronomy, they calculated the dates for new months and for leap years for the next several thousand years. With the authority of semicha-ordained rabbis, they sanctified in advance all future new months and leap years. To this day, we rely on their calendar and their sanctification when celebrating Jewish holidays.

May we soon see the day when Moshiach will once again reinstitute the Sanhedrin and our months and years will again be determined by our sages using the authority given to them by G‑d Himself!

Curious to use Hillel’s pre-calculated calendar? Check out the Date Converter!