Today is the first day of Rosh Chodesh Elul.
As we know, the names of our months aren’t original Hebrew, Rabbi Chanina tells us, “The names of the months they brought up with them from Bavel.” Ulūlu is the Babylonian/Persian version for the name Elul.
It is interesting to note that the Babylonians and Persians, also used a lunisolar calendar, where the yearly months followed the cycle of the moon, and years followed the cycle of the sun. They, like us, had a 19 years cycle, with leap years to adjust the lunar months to the solar years. The month they used to add to fill the gaps, was…. Adar, or rather Adaru. But, once in each cycle, they used to double, the month of Ulūlu.
This explains the Gemara, “The court may not intercalate the year before Rosh HaShana.” Tosfos gives the impression that it refers to adding another month of Elul!
Sources: Sanhedrin 12a; Yerushalmi Rosh Hashanah 6a.