A nice crisp word, is parapet, though the thing itself tends to be rather worrying.
Fresco by Paulo Veronese. Figures behind a parapet, about 1560.
A parapet is a wall that edges a drop, though it's usually not high enough to stop you falling over it.
Parapet's military sense is rather different, because there it is a mound of sandbags, a bank, or a rampart in front of a trench. This sort of parapet is also sometimes called a breastwork.
This is quite interesting if you know the word parapet's derivation.
Word To Use Today: parapet. This word comes from the Italian parapetto, literally chest-high wall, from the Latin pectus, breast.