The name 'Iron Age' derives from the discovery and use of a new metal technology: iron. In Wales, the earliest iron objects (750BC) come from the Llyn Fawr, Rhondda Cynon Taf, hoard. They include a sickle, a sword and a spear. The end of the Iron Age in Wales is marked by the arrival of the Romans (AD 43 onwards).

Archaeologists employ a range of dating techniques. By carefully removing soil on ancient sites, layer by layer, keeping records of what they see, it is possible to build up a history of events. By comparing objects such as pottery and metal work, found in the different layers, a sequence of changing styles emerges. Where organic materials survive, samples can be taken to be radiocarbon dated. This gives a third dimension to the dating process. Historical sources, most of which were written by the Romans with their own interpretations and biases, are rare at this time in Wales.