Notes

Archaeological evidence from sites in and around Cardiff—the St Lythans burial chamber, near Wenvoe (about four miles (6.4 km) west, south west of Cardiff city centre), the Tinkinswood burial chamber, near St Nicholas (about six miles (10 km) west of Cardiff city centre), the Cae'rarfau Chambered Tomb, Creigiau (about six miles (10 km) north west of Cardiff city centre) and the Gwern y Cleppa Long Barrow, near Coedkernew, Newport (about eight and a quarter miles (13.5 km) north east of Cardiff city centre)—shows that Neolithic people had settled in the area by at least around 6,000 BP (Before Present), about 1,500 years before either Stonehenge or the Great Pyramid of Giza was completed.A group of five Bronze Age tumuli is at the summit of The Garth (Welsh: Mynydd y Garth), within the county's northern boundary. Four Iron Age hill fort and enclosure sites have been identified within Cardiff's present-day county boundaries, including Caerau Hillfort, an enclosed area of 5.1 hectares (51,000 m2).
Until the Roman conquest of Britain, Cardiff was part of the territory of the Silures – a Celtic British tribe that flourished in the Iron Age – whose territory included the areas that would become known as Breconshire, Monmouthshire and Glamorgan. The 3.2-hectare (8-acre) fort established by the Romans near the mouth of the River Taff in 75 AD, in what would become the north western boundary of the centre of Cardiff, was built over an extensive settlement that had been established by the Silures in the 50s AD. The fort was one of a series of military outposts associated with Isca Augusta (Caerleon) that acted as border defences. The fort may have been abandoned in the early 2nd century as the area had been subdued, however by this time a civilian settlement, or vicus, was established. It was likely made up of traders who made a living from the fort, ex-soldiers and their families. A Roman villa has been discovered at Ely. Contemporary with the Saxon Shore Forts of the 3rd and 4th centuries, a stone fortress was established at Cardiff. Similar to the shore forts, the fortress was built to protect Britannia from raiders. Coins from the reign of Gratian indicate that Cardiff was inhabited until at least the 4th century; the fort was abandoned towards the end of the 4th century, as the last Roman legions left the province of Britannia with Magnus Maximus.
Little is known about the fort and civilian settlement in the period between the Roman departure from Britain and the Norman Conquest. Historian William Rees suggests that the settlement probably shrank in size and may even have been abandoned. In the absence of Roman rule, Wales was divided into small kingdoms; early on, Meurig ap Tewdrig emerged as the local king in Glywysing (which later became Glamorgan). The area passed through his family until the advent of the Normans in the 11th century.