Ever since his time there had been an armed body of Levites, kept always at hand, to guard the treasures of the temple, and to keep watch at the gates.

From these Nehemiah selects the keepers for his new gates.

Surely these Levites will be faithful, and they have had some experience in watching, inasmuch as they have for so long acted as temple police.
Nehemiah's next step was to appoint two men to superintend these guards, and to be responsible to him for the safety of the city.

At any moment he might be recalled to Persia, at any moment he might have to leave his important work in Jerusalem, that he might stand again as cup-bearer behind the king's chair.

He felt that he must therefore appoint deputies to guard the city for him, so that all might not hang upon the fact of his presence in the city.
Whom did Nehemiah choose for this post of enormous trust?
One was his brother Hanani, the very one who had come to see him in Persia.