As late as the Early Middle Ages, the Mounth, or easternmost range of the Grampian Mountains, posed a formidable terrestrial barrier isolating the northeast of Scotland from the Scottish Lowlands. This mountainous barrier, combined with the local bogs, may have been a factor in re-routing the Romans' coastal march northward, since the farthest known major coastal Roman encampment (Raedykes) in the east of Scotland, lies literally at the southern latitude of the Causey Mounth. By the twelfth century AD construction of the Causey Mounth had begun to connect these two regions of Highlands and Lowlands.