3200 BC: Cessair and followers; 2500 BC: Partholan; 2000 BC: first Nemed invasion; 1500 BC: Fir Bolg (possibly the Belgae of NW Gaul, per Julius Caesar); 1000 BC: Tuatha de Danann; 300 BC: Sons of Mil (Celts, from Spain [possibly Helvetians who had migrated from what is now Switzerland to Northern Spain]);
The first invasion of Ireland, subsequent to the coming of the Formorians, was led by a chief called Partholan: his people are known in the Irish annals as "Partholan's people." They were also probably Atlanteans.
The Formorians defeated Partholan's people, killed Partholan, and drove the invaders out of the country.
They held possession of the country for only thirty-seven years, when they were overthrown by the Tuatha-de-Dananns, a people more advanced in civilization; so much so that when their king, Nuadha, lost his hand in battle, "Creidne, the artificer," we are told, "put a silver hand upon him, the fingers of which were capable of motion." This great race ruled the country for one hundred and ninety-seven years: they were overthrown by an immigration from Spain, probably of Basques, or Iberians, or Atlanteans, "the sons of Milidh," or Milesius, who "possessed a large fleet and a strong army." This last invasion took place about the year 1700 B.C.; so that the invasion of Neimhidh must have occurred about the year 2334 B.C.; while we will have to assign a still earlier date for the coming of Partholan's people, and an earlier still for the occupation of the country by the Formorians from the West.
According to the ancient books of Ireland the race known as "Partholan's people," the Nemedians, the Fir-Bolgs, the Tuatha-de-Dananns, and the Milesians were all descended from two brothers, sons of Magog, son of Japheth, son of Noah, who escaped from the catastrophe which destroyed his country.