Middos, Chapter 1, Mishnah 8. Until now the chapter has been mapping out where the watchmen took up their stations at night and which chambers were built into the walls of the Beit Hamikdash. The Mishnah now turns back to the Beit Hamoked, the chamber kept warm by a fire, in order to finish describing how the kohanim of the watch bedded down there.
The Mishnah begins: "Beit hamoked kipah", the Beit Hamoked was roofed with a dome. This was not merely an architectural flourish. A domed ceiling was the mark of a distinguished building, the style of palaces and noblemen, and it was built that way in order to honor the kohanim who lodged beneath it.
"U'vayit gadol hayah", and it was a large structure. It had its four walls and its roof, and within it, as we learned earlier, were the four smaller chambers that opened into it.
The Stone Ledges
"Mukaf rovadin shel even", it was ringed with ledges of stone. Along the inside of the walls, stone projections jutted out, arranged so that they looked something like steps, or like low counters running around the room.
"V'ziknei beit av yesheinim sham", and the elders of the beit av slept there, stretched out on those stone projections. Who were these elders? Consider how the priestly service was arranged: the kohanim were divided into twenty four mishmarot, and each mishmar took its turn serving in the Beit Hamikdash for a full week. Each mishmar was in turn broken down into subgroups, every one of which was called a beit av, and a single beit av was charged with the avodah of one particular day of that week. When a given beit av's day came around, its senior members were accorded the distinction of taking their rest on the stone ledges.
"U'mafteichot ha'azarah b'yadam", and the keys to the courtyard gates were in their hands. The elders of the beit av held custody of the keys to the azarah.
The Young Kohanim on the Floor
"U'firchei kehunah ish kisuto ba'aretz", and the young kohanim, each man with his covering on the ground. The word pirchei comes from the sense of sprouting: these were the youngest kohanim, whose beards were just beginning to come in. They were the ones who stood watch in the Hall of Fire through the night.
Until their turn on guard duty arrived, they would lie down on the floor. Each one brought his own bedding with him, his pillow and his covers, and spread it out where he was. There were no beds and no mattresses there, nothing more than what a man standing guard would need, and when his shift came, he rose and took his post.