Middos, Chapter 1, Mishnah 9. The previous mishnah told us that the elders of each beit av held the keys to the gates of the courtyard. Our mishnah continues that thread and asks a practical question: where were those keys kept once the gates were locked for the night, and who slept beside them?
A hiding place in the floor
Inside the Beit Hamoked, the hall kept warm by the fire, the floor itself contained a recess. "Umakom haya sham": there was a certain spot there, "amah al amah", measuring one amah in each direction, a precise square. Over it lay a "tavlah shel shayish", a marble tile, turning the hollow underneath into a small concealed compartment. "Vetaba'at hayta kve'ua bah": a ring had been fixed into that tile, giving a person something to grasp so the stone could be raised. Fastened underneath hung a chain, "shehamafteichot hayu tluyot bah", and the keys of the courtyard were suspended from it.
Locking up for the night
"Higiah zman hane'ilah": when the hour for shutting the courtyard arrived, a kohein took hold of the ring, "higbia et hatavlah bataba'at", drawing the marble tile up out of the floor, and then "venatal et hamafteichot", lifting the keys off, "min hashashelet", from the chain beneath. "Vena'al hakohein mibifnim": the kohein secured the gates from within the Beit Hamoked. "Uben Levi": the Levi posted for that watch, "yashein lo", would sleep, "mibachutz", outside the hall, on the Temple Mount itself, waiting there until his turn at guard duty came around.
This arrangement reflects a pattern that runs through the Beit Hamikdash: the levi'im are always given the tafel, the secondary position, while the kohanim are given the premium one. Here the kohein is stationed inside the sheltered hall, and the Levi is stationed outside on the mountain.
"Gamar milin'ol": when the locking was done, the kohein put everything back as he had found it, "hechezir et hamafteichot lashashelet", hanging the keys again on the chain, "ve'et hatavlah limkomah", and settling the marble tile back into the floor. "Venatan kesuto aleha": he then laid his bedding right on top of the tile, "veyashan lo", and went to sleep there, so that the keys lay guarded under his own body for the whole night.
A kohein who becomes tamei during the night
Consider a kohein spending the night in the Beit Hamoked who becomes tamei through a nocturnal emission. Halachah calls such a man a ba'al keri, and his purification requires two stages: immersion, and then ha'arev shemesh, waiting for nightfall to arrive. Until that point the Temple Mount is closed to him altogether, and someone in whom this occurs while he is already standing on the mountain must leave without delay. Our kohein, though, has no easy way out, since the gates are bolted and he is the very one who bolted them. The mishnah therefore lays out the route prepared for precisely this predicament.
"Ira keri be'echad meihem": should this befall one of them, "yotzei veholech lo", he would get up from where he was lying and go to the chamber at the northwest corner of the hall, and from there enter "bamesibah haholechet tachat habirah", a passage running below the birah. Birah is the term David Hamelech applied to the Beit Hamikdash, and the mishnah adopts it here for a tunnel stretching beneath the whole Temple complex. The reason the ba'al keri was sent along this subterranean route is that the ground below does not share the kedushah of the Temple Mount above, so in walking through the tunnel he violated nothing.
"Vehaneirot dolkim mikan umikan, ad shehu magia lebeit hatevilah." Lamps burned along both sides of the passage so that his path was lit, until he arrived at the immersion chamber situated beneath the Beit Hamikdash.
The return trip and the status of a tvul yom
Having immersed, the kohein came back along the tunnel and up into that northwestern chamber, and there he waited for the gates to be unlocked at dawn. He now held the status of a tvul yom: he had gone into the water, but his day had not yet ended, so his purity was only partial. Such a person is admitted onto the Temple Mount, though the chachamim kept him out of certain precincts past it, and by that measure he should have been barred from the Beit Hamoked as well. Because he had been lodged inside the hall when the tumah came upon him, the chachamim permitted him to return to his spot after immersing and to remain there through the night, leaving the Mikdash once morning came.
"Rabbi Eliezer ben Yaakov omeir": Rabbi Eliezer ben Yaakov pictures the return journey differently. In his understanding the kohein never went back inside at all. From the immersion chamber he took a second underground route, "bamesibah haholechet tachat hacheil", a tunnel laid beneath the cheil, that band of ground ten amot across which lies just beyond the walls of the courtyard, as we studied earlier. It brought him out onto the Temple Mount, and there he stayed for the remainder of the night. Rabbi Eliezer ben Yaakov holds that a tvul yom is disqualified from entering the Beit Hamoked again, so his only recourse was to leave through the second passage and wait outside until everything was opened up.
"Yotzei veholech lo beTadi." Once the gates were opened, he left the Temple Mount and went on his way, departing through the Tadi Gate, the gate used for exiting the Temple Mount.