In ancient text, repetition is the equivalent of our modern habit of placing something in bold print as a means to draw the readers’ attention to the matter. The repetition, then, underscores the element of secrecy. Given, though, that Nehemiah wants to do an inspection, we must imagine sufficient moonlight to accomplish his purposes.
13 I went out by night by the Valley Gate to the Dragon Spring and to the Dung Gate, and I inspected the walls of Jerusalem that were broken down and its gates that had been destroyed by fire.