What roads medieval people used to cross England and Wales is a fascinating question and one that has occupied me for some time. The Ordnance Survey maps at multimap.com can show you the Roman roads. I also bought the Ordnance Survey’s Roman Britain map, precisely for this reason.
The Lancashire Antiquarian argues quite strongly for the notion that the Roman roads were used well into later periods. He writes: “It has been estimated that when the Domesday survey was taking place a minimum of 10,000 miles of usable Roman roads were still in existence in one form or another.” He states that what fell into disrepair were the bridges and river crossings, resulting in a deviation from the Roman road to a usable ford. New roads were built from medieval towns, resulting in roads that were more ‘natural’–meaning not straight or metalled.
“Roman roads, together with Roman aqueducts and the vast standing Roman army (in the 2nd century, ca. 30legions plus around 400 auxiliary units, totalling ca. 400,000 troops, of which ca. 50,000 deployed in Britain), constituted the three most impressive features of the Roman Empire. In Britain, as in other provinces, the Romans constructed a comprehensive network of paved trunk roads (i.e. surfaced highways) during their nearly four centuries of occupation (43 – 410 AD). This article focuses on the ca. 2,000 mi (3,200 km) ofRoman roads in Britain shown on the Ordnance Survey‘s Map of Roman Britain. This contains the most accurate and up-to-date layout of certain and probable routes that is readily available to the general public.
The pre-Roman Britons used mostly unpaved trackways for their communications, including very ancient ones running along elevated ridges of hills, such as the South Downs Way, now a public long-distance footpath. By the first century BC, they had begun engineering roads. After the Roman invasion, the road network was expanded. Roman roads were surveyed and built from scratch, with the aim of connecting key points by the most direct possible route. The roads were all paved, to permit even heavy freight-wagons to be used in all seasons and weather.
Most of the known network was complete by 180 AD. Its primary function was to allow the rapid movement of troops and military supplies, but it also provided vital infrastructure for trade and the transport of goods.
Roman roads remained in use as core trunk roads for centuries after the Romans withdrew from Britain in 410 AD. Systematic construction of paved highways did not resume in England until the 18th century.” http://en.wikipedia.org/wiki/Roman_roads_in_Britain
The earliest map of England that we have is the ‘Gough map’, dating to 1360. You can see it online, here. “This map of Britain was produced in C1360 and is thought to have been an official map for government use, possibly by a Royal courier, royal officer or judiciary. The distances shown are thought to be the distances following former Roman roads between the towns that where still in use during the mediaeval period. The total of the distances shown approximate to 3,000 miles, and 40% of which lie along the routes of known Roman roads” (Lancashire Antiquarian).
At the same time, David Harrison in his book, ‘The Bridges of Medieval England’ argues that this reversion to fords, beginning in the Dark Ages means that, “A road map of the eighteenth or even the early twentieth century may provide a more accurate picture of the routes of late Anglo-Saxon England than the Roman roads which are usually depicted.” (For more discussion of this book and medieval bridges, see here)
Other possibilities for discovering medieval roads in Britain are: