There was a large courtyard in Jerusalem which was called Beis Ya’azek, and there all the witnesses gathered, and the beis din interrogated them there, and made them large feasts in order that they be accustomed to come.  Originally they did not move from there all day; [then] Rabban Gamliel the Elder enacted that they should [be permitted to] walk two thousand cubits in every direction.  And not only these [witnesses], but also a midwife who comes to aid a delivery, and one who comes to rescue [people] from a fire, or from an [attacking] army, or from a [flooding] river, or from a fallen building —- they are considered like the people of the city and they have [the right to walk] two thousand cubits in every direction.