3,872. Extending the Borders of Jerusalem

Hilchos Beis HaBechirah 6:11

The borders of Jerusalem or of the courtyard may only be extended with the approval of the king, a prophet, the urim v’tumim and the Great Sanhedrin of 71 judges. This is as per Exodus 25:9: “According to all that I show you...so shall you do.” This was understood by the Sages to mean that the same rules apply in all generations. Moshe was the functional equivalent of a king.

Hilchos Beis HaBechirah 6:12

The borders of Jerusalem are extended as follows: The Sanhedrin offers two thanksgiving offerings. Two kohanim take the matzah from these and walk. The Sanhedrin followed the thanksgiving offerings. These didn’t travel together; rather, one followed the other. They stood on every corner and stone in Jerusalem, playing a variety of musical instruments and reciting Psalms 30: “I will extol you, Hashem, for You have raised me up....” They would walk until they reached the border that they wished to consecrate. There, they stood and ate one of the thanksgiving offerings, while the other was burned. A prophet would indicate which offering was eaten and which was burned.