I have made a new map showing the spread of the Hallstatt and La Tène cultures from the Late Bronze Age to the Late Iron Age.
Someday it may be possible to extend the dates in the excellent new graphic to 100 BCE and include part of Ireland for the following reasons.
All of the La Tène artifacts unearthed in Ireland have been found in the northern part. The metal finds are generally made from bronze, but in the La Tène style. Other finds are the La Tène Beehive querns found in the same general areas, but not in the exact locations. The metal objects are found in the good land and the querns are found in the poorer land. It is believed that this indicates a class distinction and indicates a population change beyond just mounted warriors.
The three principle tribes in this area were the Connachta(Féini), Ulaidh, and the Laighin and it was about these peoples that the Ulster Cycle and in particular, the Táin Bó Cúailnge were composed. In a very old law tract, we find "There were three principal kinships in Ireland: the Féini, the Ulaidh, and the Gáilni, i.e., the Laighin.".
Pronunciations:
Ulaidh = Uly; Tir Ulaidh => Ulster
Laighin = Layin; Tir Laighin => Leinster
Emhain Macha = Avan Macha
Cruachain = Cruacin
Táin Bó Cúailnge = Tawn Bo Cooley; Cattle driving of Cooley - Cooley is a peninsula in County Louth.
Work has been done in the last few decades by archaeologists who have identified two clear horizons which unite the Connachta, Ulaidh, and the Laighin by way of what are called their Royal Sites which are identified in the Táin.
These are the 'Royal Sites' of the Táin Bó Cúailnge which have been identified and studied. Emhain is the best studied and Cruachain the worst, but that is improving.
Knockaulin - Dún Ailinne of the Laighin
Tara - the most important
Navan Fort - Emhain Macha of the Ulaidh
Rathcroghan - Cruachain of the Connachta
Horizons (summarized):
4th century BCE - late second BCE: A series of figure-of-eight structures are built in Emhain, Dún Ailinne and Tara. (Unknown at Cruachain). They have no parallel anywhere in Europe.
1st century BCE (95 BCE at Emhain by dendrochronology): The figure-of-eight structures are removed and a "40 meter structure" is built at all 4 sites. They have no parallel anywhere in Europe.
It seems that the archeology reveals a direct prehistoric datable connection among the Connachta, Ulaidh, and the Laighin which parallels the stories of the Ulster Cycle. This may mean something about the spread of La Tène and possibly M222.