Adam Clarke on Ezekiel 42:20

It had a wall round about - to make a separation between the sanctuary and the profane place - The holy place was that which was consecrated to the Lord; into which no heathen, nor stranger, nor any in a state of impurity, might enter. The profane place was that in which men, women, Gentiles, pure or impure might be admitted. Josephus says War, lib. vi., c. 14, that in his time there was a wall built before the entrance three cubits high, on which there were posts fixed at certain distances, with inscriptions on them in Latin and Greek, containing the laws which enjoined purity on those that entered; and forbidding all strangers to enter, on pain of death. See Calmet.