'Flags' in the Bible

And when she could not longer hide him, she took for him an ark of bulrushes, and daubed it with slime and with pitch; and she put the child therein, and laid it in the flags by the river's brink.

And the daughter of Pharaoh came down to bathe at the river; and her maidens walked along by the river-side; and she saw the ark among the flags, and sent her handmaid to fetch it.