Periodisation
At present over 100 large-scale excavations of Iron Age sites have taken place, dating from the 8th century BC to the 1st century AD, and overlapping into the Bronze Age in the 8th century BC. Hundreds of radiocarbon dates have been acquired and have been calibrated on four different curves, the most precise being based on tree ring sequences.
The following scheme summarises a comparative chart presented in a 2005 book by Barry Cunliffe, but it should be noted that British artefacts were much later in adopting Continental styles such as the La Tène style of Celtic art:
| Earliest Iron Age | 800-600 BC | Parallel to Hallstatt C on the continent |
| Early Iron Age | 600-400 BC | Hallstat D and half of La Tène I |
| Middle Iron Age | 400-100 BC | The rest of La Tène I, all of II and half of III |
| Late Iron Age | 100-50 BC | The rest of La Tène III |
| Latest Iron Age | 50 BC - AD 100 |
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The end of the Iron Age extends into the early Roman Empire under the theory that Romanisation required some time to effect. In parts of Britain that were not Romanised, such as Scotland, the period is extended a little longer, say to the 5th century. The geographer closest to AD 100 is perhaps Ptolemy. Pliny and Strabo are a bit older (and therefore a bit more contemporary), but Ptolemy gives the most detail (and the least theory).
Read more about this topic: British Iron Age