A waterless ditch outside the wall is called a huáng.
Tips
culture
Most learners meet this character only in 城隍 - the City God, a tutelary deity guarding a walled town. The pairing is literal: 城 is the wall and 隍 its dry protective ditch, together standing for the town's defenses.
memory
The mound radical 阝 (here a left-side earthwork) plus 皇 for the sound: picture an imperial earthen rampart with an empty trench at its foot - a moat with no water.
On the left this is the mound radical, a compressed form of 阜 ('earthen hill'). It signals earthworks and terrain, exactly right for a ditch dug around a city wall.
