Historically The Mounth was a formidable barrier which, to some extent, isolated the northeast of Scotland from the Scottish Lowlands, physically and culturally. In the Middle Ages an ancient roadway known as the Causey Mounth was built to connect Stonehaven to Aberdeen using an elevated rock causeway design to penetrate this boggy area of the eastern Mounth. This route was by way of Cowie Castle, Muchalls Castle, Portlethen Moss and the Bridge of Dee. The route was that taken by Earl Marischal and the Marquess of Montrose when they led a Covenanter army of 9000 men in the first battle of the Wars of the Three Kingdoms in 1639.