Shevuos, Chapter 2, Mishnah 2. This mishnah deals with the areas included in the definition of the Beis HaMikdash, which a person who is tamei may not enter. As we have learned, the penalty of kareis applies to one who enters the Azarah - the courtyard of the Beis HaMikdash - while tamei, and not to one who enters the Har HaBayis; a person who is tamei from contact with a corpse does not become liable for entering the Har HaBayis, rather the Azarah itself is the place that carries liability, as does any area properly annexed to it.
From here the mishnah turns to a further matter: there are areas within the Azarah that were not part of it originally, but were added to it. The mishnah describes the process through which an area can come to be considered halachically part of the Azarah.
"Ein mosifin al ha'ir ve'al ha'azaros":
Jerusalem has its own special set of halachos, different from the area outside it, and therefore there is a precise halachic distinction as to what counts as being inside Jerusalem. One who wishes to add to the area of the city, and likewise one who wishes to add to the Azaros, must follow an ordered process, and these are its components:
A king - the process is carried out only with a king.
A prophet.
Urim VeTumim - the instrument of communication with the Holy One, Blessed is He, worn by the Kohen Gadol.
Sanhedrin - the Great Sanhedrin of seventy-one.
Two todah offerings - the two loaves of the thanksgiving offering.
Song - the Levites sing as part of the process.
The order of the procession:
The mishnah states: "U'beis din mehalchin u'shtei todos achareihen" - the seventy-one members of the beis din walk around the perimeter, and the two loaves of the thanksgiving offering come after them. The Gemara, however, explains that the mishnah means that the beis din walks and the two todos walk, but in practice the beis din walks behind the two todos, and the rest of the Jewish people walk behind the beis din.
Of the two todos - "hapenimis ne'echeles vehachitzonah nisreferes" - and the Gemara teaches that this was a directive of the prophets: it was the prophets who commanded that one be eaten and one be burned.
What is this "inner" one?
In the Gemara the Amoraim disagree as to how the loaves were carried:
According to one opinion they were carried together, side by side, and therefore the inner one is the loaf closer to the new wall, since the procession went along the outside of the wall.
According to the second opinion they were carried one behind the other, and therefore the inner one is the second loaf, the one carried closer to the beis din walking behind them.
Adding to the city and adding to the Azarah:
The Gemara clarifies that although the Mishnah mentions the loaves of the thanksgiving offering, they were used only when adding on to Jerusalem and not when adding on to the Azarah, and this is the reason:
When adding on to Jerusalem - the thanksgiving offering is eaten anywhere within Jerusalem, and therefore, to mark the addition to the city, one takes something that is eaten throughout Jerusalem and only there.
When adding on to the Azarah - one must use something that is eaten only in the Azarah, and therefore this was done with the remnants of a minchah, the leftovers of the flour offering, which may be eaten only in the courtyard of the Beis HaMikdash.
The Mishnah concludes: "V'chol shelo ne'esah b'chol elu - hanichnas l'sham ein chayavin alehah" - any place that was not sanctified with all of these conditions, one who enters it in a state of tumah does not become liable to bring a korban.
It is worth noting that in the second Beis HaMikdash there was no king and there were no Urim v'Tumim, and nevertheless the place was sanctified, because its original sanctity from the days of King Shlomo sanctified it for all time as well. And although we find in the verses that such a procedure was carried out in the days of the second Beis HaMikdash, it was done only as a commemoration of what had taken place in the days of the first Beis HaMikdash.