Hillel II

Hillel II (Hebrew: הלל השני) was a Jewish sage and Nasi (Prince) of the Sanhedrin during the Amoraic period. He is credited with standardizing the Jewish calendar, a crucial development in Jewish religious observance.

Prior to Hillel II, the Hebrew calendar was luni-solar and regulated by observation. The Sanhedrin in Israel determined the start of new months based on eyewitness testimony of the new moon and adjusted the calendar with leap months to align it with the solar year, preventing Jewish holidays from drifting seasonally. Messengers were then dispatched to Jewish communities outside of Israel to inform them of the fixed dates.

However, in the 4th century CE, facing increasing persecution under Roman rule and anticipating the dissolution of the Sanhedrin, Hillel II foresaw the difficulties Jewish communities would face in coordinating the calendar without a central authority. To ensure uniformity and prevent potential disagreements, he established a fixed, arithmetical calendar based on mathematical calculations. This calendar incorporated a 19-year cycle with specifically placed leap years.

This permanent calendar, essentially the one still in use today, allowed Jewish communities worldwide to observe holidays at the same time without relying on communications from the Sanhedrin or observation of the new moon in Israel. It represents a significant act of leadership and foresight, contributing to the continuity and unity of Jewish practice. While the exact methods Hillel II used are debated, his contribution in formalizing the calendar remains a cornerstone of Jewish life.