Hill forts were a significant part of the Iron Age in Wales, which occurred during the 500 years leading up to the Roman conquest of Britain.  “The earliest iron artefact in Wales is a sword dating to about 600 BCE, but by 400 BCE iron was being smelted and crafted into tools all over the British Isles.

The tribes of Wales developed regional styles of working iron, gold, and other metals, following the exquisite western European style known as La Tene (after the village of La Tene in Switzerland). At the same time as iron was introduced to Britain a new crop of settlers arrived from northern Europe.”  http://www.britainexpress.com/wales/history/iron-age.htm   This new group were the Celts.  They overran the whole of Britain, whether by conquering the then-native peoples, or gradually settling the country over a period of time.

According to the National Museum of Wales, there are over 1000 iron age hillforts in Wales (though some could be more aptly viewed as ‘defended farms’).

• Hillforts are fortified enclosures built of earth, timber or stone and frequently sited on defensible hilltops. They were built from the Late Bronze Age, throughout the Iron Age (1100BC-AD50) and some were also occupied during Romano-British times. They enclose areas of between 0.1 and 80 hectares, although in Wales most are under 2 hectares in area.
• Hillfort defences usually consist of a bank (rampart) made of material dug from an outer ditch. Some hillforts were provided with additional defences. Many hillforts have elaborate and strengthened entrances incorporating impressive gate structures.
• More recently, a number of archaeologists have emphasised the great diversity in hillfort characteristics. They argue for a number of different roles, not merely defensive ones. Many hillforts are sited in poorly defensive locations, others do not seem to have been lived in continuously or intensively. Instead, they may have acted as stock enclosures, agricultural fair grounds and religious centres at certain times of the year. As monuments, they may have been as much about displaying the status and power of different community groups, as they were about defence. A large number of small hillforts in Wales should essentially be seen as single farms occupied by small family groups.  http://www.museumwales.ac.uk/en/2370/

Three hill forts of particular interest that cover the whole range of styles and periods are Dinas Bran, Dinas Emrys, and Tre’r Ceiri.

The ruins that sit atop Dinas Bran (meaning literally, “Hill of the Crow”, or “Bran’s Stronghold”) were built in the medieval period, but the site was continuously occupied from the Iron Age and the ditch and earthen embankments visible today date from that initial settlement.  http://www.castlewales.com/dinas.html

“The hillfort has a single bank and ditch enclosing an area of about 1.5 hectares. To the south and west the defences are most considerable being up to 8 metres high in places. The entrance lies in the south-west corner of the fort and is defended by an inward curving bank. To the north the fort is defended by the natural steepness of the land and no earthwork defences were required.”  http://www.cpat.org.uk/educate/guides/dinasb/dinasb.htm

Dinas Emrys sits atop a rock that is one of the strongest, natural fortifications in Wales.  Modern archaeology reveals: “Dinas Emrys was occupied to some extent in the late Roman period, but that rough stone banks around its Western end are later. They were poorly built of stone two or three times and took strategic advantage of natural crags. Still less substantial walls were also discovered to the north and south. Broken sherds of Eastern Mediterranean amphorae, Phoenician red slip dishes and a pottery lamp roundel featuring a Chi-Rho symbol indicate that these features do indeed date to the 5th and 6th century.”
http://www.earlybritishkingdoms.com/archaeology/emrys.html
http://www.castlewales.com/dinas_em.html

The last site, Tre’r Ceiri is a spectacular iron age site, located on the Llyn Penninsula in Wales. A climb to the top of the 457 meter hill reveals 150 hut circles still clearly discernable, capable of housing upwards of 500 people. The stone walls surrounding the fort were 4 meters (12+ feeet) high in places and the huts range in size from 3 meters to 8 meters across.