Albert Barnes Commentary Nehemiah 2:15

"Then went I up in the night by the brook, and viewed the wall; and I turned back, and entered by the valley gate, and so returned." — Nehemiah 2:15 (ASV)

The brook - The Kidron watercourse, which skirted the city on the east.

Turned back - that is, he turned westward, and having made the circuit of the city, re-entered by the valley-gate.