A sunken lane is a road or track that is significantly lower than the land on either side, not formed by the engineering of a road cutting but possibly of much greater age. Various mechanisms have been proposed for how holloways may have been formed, including erosion by water or traffic; the digging of embankments to assist with the herding of livestock; and the digging of double banks to mark the boundaries of estates. These mechanisms are all possible and could apply in different cases.
Means of formation
A variety of theories have been proposed for the origins of holloways. Different mechanisms may well apply in different cases.
Erosion
Some sunken lanes are created incrementally by erosion, by water and traffic. Some are very ancient with evidence of Roman or Iron Age origins, but others such as the Deep Hill Ruts in the old Oregon Trail at Guernsey, Wyoming developed in the space of a decade or two. Where ancient trackways have lapsed from use, the overgrown and shallow marks of hollow ways through forest may be the sole evidence of their former existence. On disused ridgeways in central Germany, the hollow ways often mark inclines. The earth banks on either side, sometimes topped with hedges and trees, can give the impression of a tunnel enclosing the traveller. Because the roadway is restricted by the banks on either side, sunken lanes typically admit the passage of only one vehicle; that is, they are single track roads. Occasional passing places may be provided, but a meeting of vehicles in a sunken lane often requires one party to reverse to a suitable passing place. In Central Germany, "dual carriageways" have been observed with two trenches side by side where a trackway was in such heavy use that it had lanes dedicated for each direction.
Embankments for cattle
Up to the present day, some writers have assumed that low banks were deliberately created with shovels as a means to hem in cattle, but there is no evidence for this, and in any case, banking only appears intermittently in certain types of soil. When metalled, sunken lanes are unlikely to erode any further down.
Double boundary banks
In The Making of the English Landscape, W. G. Hoskins explains the origin of some English holloways as a pair of matched earth banks marking the boundaries of two landowners' estates, as evidenced by the "two-fold ditch", twifealda dich in a charter of c. 1174 describing the boundary between the abbot of Tavistock's land at Abbotsham, Devon and Richard Coffin's land at Alwington and Cockington. He gives another example, also from Devon, in a photograph of Armourwood Lane, Thorverton, which bounded the royal Silverton estate and the estate of Exeter abbey, most likely in the seventh century. Hoskins states that some such lanes are Celtic, some Saxon, some mediaeval.
In different countries
Belgium
A sunken lane extending across the battlefield played an important role in the Battle of Waterloo in 1815, particularly in presenting an obstacle to the French cavalry. Victor Hugo dramatized this episode in Les Misérables.
One of the largest networks of such routes in Germany is to be found in the municipalities of Alsheim and Mettenheim in Rhineland-Palatinate, where there they make up over 30 km of hiking trails. Some of these sunken lanes can be up to 5 metres deep.
Spain
In Galicia and western Asturias the sunken lanes are usually called congostras or corredoiras, from Latin coangusta 'confined' and curro, currere 'run', being a common and characteristic feature of rural areas. Some lanes are now being recovered as hiking trails.
United States
Aside from the Oregon Trail, sunken roads are found in states along the Atlantic seaboard, where European settlement began in the 17th century. In the Baltimore and Washington, D.C. areas, some sunken roads dating to that era have become busy suburban routes whose high embankments testify to their long history of traffic. A sunken road played a major role in many military operations, such as the American Civil War battles at Antietam, Fredericksburg, and Shiloh.
In Syria, faint traces of hollow ways attest to a dense network of tracks or paths connecting Bronze Age sites with each other and with their cultivation zones in the fourth and third millennia BC, and thousands of kilometres of such routes have been surveyed.
United Kingdom
Sunken lanes are a characteristic feature of the landscape of southern England, especially in the chalk areas of the North and South Downs, and greensand areas such as the Weald. The Surrey Hills AONB has many sunken lanes. Seal Hollow Road in Sevenoaks is a fine example of a sunken lane in southern England. They are a particular feature of the West Country, in counties such as Dorset, and west Wales – areas unaffected by the land enclosures of mediaeval England. The English name holloway derives from the Old English "hola weg", a sunken road. While many sunken lanes are now metalled, some are still unsurfaced green lanes, typically now designated as either bridleways or byways. A sunken road is a cross country equestrian obstacle.
