3,890. Where Leviim Stood Guard

Hilchos Beis HaBechirah 8:8

The Leviim stood guard inside the five gates to the Temple Mount, at its four corners on the inside, outside the four corners of the courtyard – because it is prohibited to sit in the courtyard – and outside five of the gates to the courtyard. Kohanim stood watch at the hearth chamber and the spark gate (which were the other two gates). This makes eighteen places where the Leviim stood guard.

Hilchos Beis HaBechirah 8:9

The other three places where the Leviim stood guard were the sacrifice chamber, the curtain chamber and behind the Holy of Holies.