Matthew Poole and continuators on 1 Chronicles 9:18

18 (Who hitherto waited in the kings gate eastward) They were porters in the companies of the children of Levi.

In the East-gate of the Temple, which was so called, either because it was the Chief and most Magnificent of all the Gates: or because the Kings of Iudah used to go to the Temple through that Gate, 2 King. 16. 18. Compare Ezek. 44. 1, 2. Under this Gate he comprehends all the rest, which also were guarded by these Porters.

Or, according to the companies, or orders, or courses, i. e. They kept the Gates successively according to that Method into which themselves and the rest of their Brethren the Levites were distributed for the more convenient management of their several Offices; among which this of the Porters was one.