A recessed trench wall known as a ha-ha has been built to minimize the visual impact of a security barrier surrounding the monument . After the September 11 attacks and another unrelated terror threat at the monument , authorities had put up a circle of temporary Jersey barriers to prevent large motor vehicles from approaching . The unsightly barrier was replaced by a less-obtrusive low granite stone wall that doubles as a seating bench and also incorporates lighting . The installation received the 2005 Park/Landscape Award of Merit from the American Society of Landscape Architects
September 11 attacks
September 11 attacks
Washington Monument