The Causey Mounth is an ancient drovers' road over the coastal fringe of the Grampian Mountains in Aberdeenshire, Scotland. This route was developed as the main highway between Stonehaven and Aberdeen around the 12th century AD and it continued to function as the principal route connecting these two cities until the mid 20th century, when modern highway construction of the A90 road occurred in this area. There are extant paved and usable sections of this road over part of the alignment; however, many parts of the ancient route are no more than footpaths, and in some cases the road has vanished into agricultural fields. Constructed in the Middle Ages, the Causey Mounth was created as an elevated rock causeway to span many of the boggy areas such as the Portlethen Moss.