Several Iron Age sites have been found in the City and County of Cardiff.
They are: the Castle Field Camp, east of Graig Llywn, Pontprennau; Craig y Parc enclosure, Pentyrch; Llwynda Ddu Hillfort, Pentyrch; and Caerau Hillfort—an enclosed area of 5.1 ha (13 acres). The area to the south east of the Fosse Way—between modern day Lincoln and Exeter—was under Roman control by 47 AD.
As Great Britain became heavily wooded, movement between different areas was restricted, and travel between what was to become known as Wales and continental Europe became easier by sea, rather than by land.
People came to Wales by boat from the Iberian Peninsula.
Four Neolithic burial chambers stand within a radius of 10 mi (16 km) of Cardiff City Centre, with the St Lythans burial chamber the nearest, at about 4 mi (6.4 km) to the west.
Bronze Age tumuli are at the summit of Garth Hill (The Garth; Welsh: ), within the county's northern boundary, and four Iron Age hillfort and enclosure sites have been identified within the City and County of Cardiff boundary, including Caerau Hillfort, an enclosed area of 5.1 ha (13 acres).
Nicholas, Vale of Glamorgan (about 6 mi (9.7 km) west of Cardiff City Centre), the Cae'rarfau Chambered Tomb, Creigiau (about 6 mi (9.7 km) northwest of Cardiff City Centre) and the Gwern y Cleppa Long Barrow, near Coedkernew, Newport (about 8.25 mi (13.28 km) northeast of Cardiff City Centre)—shows that these Neolithic people had settled in the area around Cardiff from at least around 6,000 BP, about 1500 years before either Stonehenge or The Egyptian Great Pyramid of Giza was completed.
British tribes from beyond this new frontier of the Roman Empire resisted the Roman advance and the Silures, along with Caratacus (Welsh: Archaeological evidence shows that a settlement had been established by the Silures in central Cardiff in the 50s CE, probably during the period following their victory over the Roman army.
The settlement included several large timber framed buildings of up to 45 m (148 ft) by 25 m (82 ft). Until the Romans established their fort, which they built on the earlier Silures settlement, the area that would become known as Cardiff remained outside the control of the Roman province of Britannia.
Doggerland was submerged by the North Sea and, by 8000 BP, the British Peninsula had become the island of Great Britain.
John Davies has theorised that the story of Cantre'r Gwaelod's drowning and tales in the Mabinogion, of the waters between Wales and Ireland being narrower and shallower, may be distant folk memories of this time.