Monuments shall be placed at all block corners, angle points, points of curves in streets and at intermediate points as shall be required by the City Engineer. Permanent monuments erected in such subdivisions of galvanized iron pipe or iron pipe shall be not less than one-half inch (½") in diameter and thirty inches (30") in length; and if stone or concrete, shall not be less than four inches (4") in diameter and twenty-four inches (24") in length.