Middos, Chapter 1, Mishnah 5. This mishnah picks up exactly where the previous one left off. There we learned that the courtyard of the Beit Hamikdash was surrounded by a wall on all four sides, and we began listing the gates that opened into it. Now the mishnah continues that tour, moving along the northern wall.
"Veshebatzafon" - and in the north. Counting from the west, the first gate was Sha'ar Hanitzotz, the Gate of the Spark. It carried that name because a fire was kept burning there at all times, held in reserve in case the fire on the mizbeach went out and needed to be rekindled.
"Ukhemin akhsadra hayah va'aliyah benuyah al gabav" - it was shaped like an open foyer with an upper chamber built above it. That is, the gate had a wall on either side, while the space in front of it stood open rather than closed in. Above this foyer was a second story, and there the kohanim would keep watch.
"Shehakohanim shomrim milma'lan vehaleviim milmatan" - the watch of the kohanim was kept on the upper level, while the Leviim stood guard below. Why the split? It reflects their standing: a Levi ranks under a kohen. Wherever the two were assigned to one and the same post, the kohen took the elevated place and the Levi remained at ground level, on the floor of the Har Habayit. First honor goes to the kohen.
"Upetach hayah lo lacheil" - this foyer also had an opening leading out to the cheil, the strip ten amot wide that ran just outside the courtyard. We will return to the cheil in greater detail later in the masechet.
"Sheni lo Sha'ar Hakorban" - proceeding past the Gate of the Spark, one came to the Gate of the Offering. Its name reflects its use: this was the entrance through which animals designated as kodshei kodashim, sacrifices of the highest sanctity, were led in, for their shechitah had to be performed on the north side of the azarah.
"Shelishi lo Beit Hamoked" - the third gate, continuing from the Gate of the Spark, was the Chamber of the Hearth. This was a large hall in which fires burned constantly. The kohanim served in the Beit Hamikdash barefoot, and their feet would grow cold, so the fires of this chamber were there to warm them.