Both topography and geography change over time. Geologically, Wales hasn’t changed much in 2000 years, but the topography has, from mining, from the building of villages and cities, and from the wholesale cutting–and then replanting–of forests. As evidenced by the loss of the location of many of the Roman roads, transportation routes change over time. What used to be on a major pathway across the country is now in a desolate, hard-to-reach area.
As one example, in Powys, in the 19th century, the leader of Birmingham City Council set about finding a clean water supply for the City. He identified the Elan and Claerwen Valleys as having the best potential for water storage with ample water (72 inches a year), narrow downstream valleys, impermeable bedrock, and a higher altitude eliminating the need for pumps.
“An Act of Parliament was passed for the compulsory purchase of the area and in 1893 the building work began. Over 100 occupants of the Elan Valley had to move, only landowners received compensation payments. Many buildings were demolished, among them 2 manor houses, 18 farms, a school and a church (which was replaced by the corporation as the Nantgwyllt Church). A railway line was constructed to transport the workers and thousands of tonnes of building material each day and a village of wooden huts was purpose built to house many of the workers on the site of the present Elan Village.” http://www.rhayader.co.uk/index.php/rhayader/aboutdetail/the_surrounding_area/
It is maps that can clarify these changes. These are administrative maps dating from the time of Rhodri the Great (900s AD), to the 13th century AD under Llywelyn ap Gruffydd, to modern administrative jurisdictions:
Then there are maps of important castles in Wales. This one is from the fabulous castlewales.com web page (http://www.castlewales.com/native.html).
It doesn’t have Aber Garth Celyn on it or Aberffraw, both of which were destroyed after 1282, though it does have Deganwy. My assumption is that this map may be old–and it is an important point that what is mapped can reveal as much about the map maker as the place he/she is mapping:
This map shows similar information, and also doesn’t include King Edward’s castles (King Edward ruled Wales after the murder of Llywelyn ap Gruffydd, the last Prince of Wales, in December of 1282). It’s from the Welsh government site (cadw.wales.gov.uk):
This is Roman road map (for construction between 44-410 AD) of Wales (not very good–the paper Ordnance Survey map is far better). What this map doesn’t show as clearly is that many of the modern roads do not follow the Roman roads–whether because of the differences is in road building techniques or because the relative importance of various destinations has changed. This is particularly evident with the Roman road that went from Tomen y Mur through Dolwyddelan to Caerhun. There’s not even a track that follows that exact route anymore. There’s also evidence indicating that another road not on this map ran south from St. Asaph through Ruthin and connected with the road running from Caer Gai to Chester. Another ran south from Caer Gai to Caersws, and connected to the roads at Castell Collen.