Rosh Hashanah, Chapter Two, Mishnah 5. This mishnah deals with the way in which the witnesses who saw the new moon would gather in Jerusalem, and with the halachah that applied to them when they arrived from outside the techum on Shabbos.
The text of the mishnah:
"Chatzer gadol hayah biYerushalayim uveis Yaazek hayah nikra" - there was a large courtyard in Jerusalem, and its name was Beis Yaazek.
"Lesham kol ha'edim miskansim" - all the witnesses who came to testify about the sighting of the new moon would gather there.
"Uveis din bodkin osam sham" - in that courtyard the beis din would examine the witnesses and question them about what they had seen.
"Use'udos gedolos osin lahem bishvil sheyehu regilim lavo" - large meals and feasts were prepared there for the witnesses, in order to encourage them and accustom them to come and testify.
Witnesses who came from outside the techum:
"Barishonah lo hayu zazim misham kol hayom" - at first the witnesses would not leave the courtyard for the entire day. The witnesses were permitted to come from outside the techum on Shabbos, as we have already learned that one may desecrate Shabbos for the sake of testimony about the sighting of the new moon. However, the halachah is that one who has gone outside the techum has only four amos. When he finds himself in an enclosed area, that entire area counts as his four amos, but he may not leave it. For this reason the witnesses were required to remain within the courtyard.
The enactment of Rabban Gamliel the Elder:
"Hiskin Rabban Gamliel hazaken sheyehalchu alpayim amah lechol ruach" - Rabban Gamliel the Elder instituted a new enactment, that the status of the witnesses should be like the status of the residents of the city, and that they should have two thousand amos in every direction outside the city, just as the residents of the city may go two thousand amos beyond it. For the residents of the city this is no leniency at all, but for the witnesses who came from outside the techum it is a complete leniency.
"Velo elu bilvad":
Not only the witnesses who came to testify about the new moon were included in this halachah, but also those who came for the sake of other mitzvos:
"Af hachachamah haba'ah leyaled" - a midwife who comes to desecrate Shabbos in order to help a woman give birth.
"Haba lehatzil min hadeleikah umin hagayis" - one who comes to save people from a fire or from an invading army.
"Umin hanahar" - from a river that has overflowed its banks.
"Umin hamapoles" - from a building that has collapsed, such as in an earthquake.
"Harei elu ke'anshei ha'ir veyesh lahem alpayim amah lechol ruach" - anyone who went outside the techum for the sake of one of these mitzvos of rescue has the status of the residents of the city, and he has two thousand amos in every direction from the city, exactly like the law of those who live there.
In summary: in this mishnah we learned about Beis Yaazek, the large courtyard in Jerusalem to which the witnesses would gather and in which the beis din examined them, and about the meals that were served there in order to accustom the witnesses to come. We also learned that at first the witnesses who came from outside the techum were forbidden to move from the courtyard the entire day, until Rabban Gamliel the Elder enacted that they should have two thousand amos in every direction, and that this enactment was stated as well regarding those who come for the sake of mitzvos of rescue: the midwife, and one who comes to save from a fire, from an invading army, from a river and from a collapsed building.