Hillforts Dun Alyn and Dun Dreug are imaginary places, but they are based on what we know about real fortresses of Britain. These strongholds usually began as simple walled structures for one or two families and were called duns. By the time the Romans invaded Britain in 43 AD, many of these duns had grown into large fortresses. They were usually located on hilltops or on headlands jutting out into the sea because these sites were easiest to defend. A fortress might be surrounded by as many as three rings of earth and ditches outside a wooden or stone wall. If the compound were located on a cliff or a piece of land that jutted out into the sea, it would only need defensive rings on the side that faced land. Some of the fortresses were large enough to shelter as many as 3000 people, though many were smaller. The chief would probably have ruled over about 25 square miles of territory around the fort.
During the three hundred years that the Roman Empire controlled most of Britain, the hill fortresses were abandoned in the South because Roman forts and cities provided protection for the population. In the North, however, the Romans did not control the area so hill fortresses continued in use and probably became larger and stronger because of occasional threats from the Roman troops. Many hillfort sites are marked on maps and can be visited today by anyone willing to walk up a steep incline. It is an eerie feeling to stand on one of these deserted spots, surrounded by remains of walls and hut circles, and look out across the countryside. On the seaside locations, the visitor today can stand, just as Ilena did 1500 years ago, and look down steep cliffs to the sea crashing against the rocks.
Walls Rome had built a fortification of stone called Hadrian's Wall across Britain from the Solway Firth on the west to the mouth of the Tyne River on the east beginning in 122 AD. An earthen one, the Antonine Wall, running from the Firth of Forth to the Firth of Clyde in what is now Scotland, was started a few years later. The Antonine Wall had little effect and fell into disrepair after a short time, but Hadrian's Wall, with its fortresses and small forts and watch-turrets, kept the Roman area across the South of Britain separated from the old Celtic way of life in the North for nearly 200 years.
Roundhouse photo from Hadrians Wall Education Website - http://museums.ncl.ac.uk/wallnet/wall