Mesiba beneath the bira

The underground passage of the kohen on watch who became impure during the night. From the north-west chamber of the Beit HaMoked, a spiral of steps sinks beneath the Azara; a tunnel lit by lamps on both sides leads to the Beit HaTevila. The bira is the whole Mikdach, and the mesiba runs beneath it. It is not sanctified — a tunnel opening onto the Har HaBayit is not — which is why the impure kohen may walk through it.

Dimensions

• start: the north-west chamber of the Beit HaMoked, on the non-sacred side
• a spiral of thirty half-ama steps and a last step down to the tunnel floor, fifteen and a half amot below the Azara
• a tunnel 3.5 amot wide and 5 high, lamps on both sides
• southward, then westward beneath the Beit HaMitbachayim, to the Beit HaTevila

Sources

• Middot 1:6“צְפוֹנִית מַעֲרָבִית, בָּהּ יוֹרְדִים לְבֵית הַטְּבִילָה”
• Middot 1:9“יוֹצֵא וְהוֹלֵךְ לוֹ בַמְּסִבָּה הַהוֹלֶכֶת תַּחַת הַבִּירָה, וְהַנֵּרוֹת דּוֹלְקִים מִכָּאן וּמִכָּאן, עַד שֶׁהוּא מַגִּיעַ לְבֵית הַטְּבִילָה”
• Tamid 1:1
• Bartenura Middot 1:9“וְכָל הַמִּקְדָּשׁ קָרוּי בִּירָה”
• Rambam, Hilchot Beit HaBechirah 5:11“הָיָה הוֹלֵךְ בַּמְּסִבָּה הַהוֹלֶכֶת תַּחַת הַמִּקְדָּשׁ כֻּלּוֹ”
• Rambam, Hilchot Beit HaBechirah 8:7“שֶׁהַמְּחִלּוֹת הַפְּתוּחוֹת לְהַר הַבַּיִת לֹא נִתְקַדְּשׁוּ”
• Tamid 27b“מְחִילּוֹת לֹא נִתְקַדְּשׁוּ”

Project decisionSet aside: the view of R. Eliezer ben Yaakov, who runs the tunnel beneath the Cheil and has the kohen exit through the Tadi gate (Middot 1:9); the Rambam and Bartenura do not follow him. Tour's choice: the route, width and height of the tunnel, the shape of the descent and the spacing of the lamps.