John Gill Commentary 1 Chronicles 9:18

"who hitherto [waited] in the king`s gate eastward: they were the porters for the camp of the children of Levi." — 1 Chronicles 9:18 (ASV)

Who hitherto waited in the king's gate eastward
At the gate through which the king went into the temple, and was at the east of it; and here these porters were placed in the same order after the captivity, and their return from it, as before:

they were porters in the companies of the children of Levi ;
or in the camp of Levi, which was placed around the tabernacle, as in the wilderness: the Septuagint version is, "these are the gates of the camp of the children of Levi"; at which these porters were placed.