Rosh Hashanah 23 - Insecure telegraph
Initially the Court had a quick system of announcing the New Moon: they would light torches to let the next station know, and in five hops the news was transmitted to the whole Diaspora (really, the city of Pumbedita), which looked as if aflame with fire.
The calendar month could only have one of the two: either twenty-nine or thirty days. If the month was short (twenty-nine days), they made it known with torches, and if it was long (thirty), then nothing had to be done. However, this system was based on trust and open to hacking; the followers of a certain sect led by Baitus messed it up by hiring witnesses, with the desire to mislead the Sages. It was then established to accept testimony from known people. They also lit their own torches, to confuse the court, and when this was uncovered, the Sages instituted sending messengers.
We mentioned before that the establishment of the New Moon would also determine the dates for the Holidays. This was so important that the witnesses who would come to testify about having seen the new moon were allowed to violate Shabbat. Therefore, when they came to Jerusalem, they could be outside the area of two thousand steps which one can travel on Shabbat. They would sit in a big courtyard, established for this purpose, and enjoy festival meals prepared for them. Still, it was too restrictive, and Rabban Gamliel changed the law to allow them to go to any place in Jerusalem.
Art: New Moon by Maxfield Parrish