"All who are adepts in Druidical and magical arts are the descendants of the Tuatha De Danaan."
At the time of the Ice age to the coming of the Celts it was a time on the verge of pre-history. That is to say when written records were scant. That is not to say that legends do not sufficently fill in the gaps though...
The Legend of the Tuatha De Danna
When Tir Nan Og went under the waves the Tuatha de Danan dispersed in fleets of ships, eventually settling in Ireland. From the land of Og they rescued four relics:
The Lia fail (the stone of destiny). Kings would be crowned on this stone.
They brought the sword of Nuada, this would later become known as Excalibur.
They brought the spear of Lugh which would be later be better known as the spear of destiny.
They brought the cauldron of Dagda which would later be known as the holy grail.
They are said to of landed in a great mist upon the Iron Mountain's or Sliev-an-lerin , in County Leitrim.
Once there they burned their ships, symbolising that there was no going back, now they were going to either make Eiru their home or die trying.
Some have speculated that the Legend of Atlantis is connected to the Tuatha De Dannan's arrival, namely that they were either reminants of Atlantis itself or an outpost colony who set out with the rising sea-levels to safer lands.
According to an eyewitness account given in the Book of Billamote a source named Fintan said:
"After them, the Tuatha De arrived
Concealed in their dark cloud
I ate my food with them
Though at such a remote period."
According to the annals of the four masters (a historical document) it was about 1997 BC.
The Tuatha De Dannan did not arrive to an empty Island, Eire was inhabited even back in those days (pre 6000 BC), it's people were led by Fir Bolg and the Fomorian's, giant creatures.
The latter of which had a formidable giant creature called Balor as their guardian.
Although the Tuatha were outnumbered and against overwhelming odds they did have the edge in technology and artifacts.
The legend's speak of them being able to cloak themselves in 'mist', enabling them to confuse and overcome their enemy by stealthy skirmishes and surprise attacks.
First fighting and defeating the Fir Bolg was no mean feat, for these beings were even stronger than the Tuatha were. During the clash of battle Sreng, the Fir Bolg champion, managed to cut off King Nuada's hand in single combat. As the Tuatha King fell back his bodyguard surged forward along with the Morrigan, the Tuatha's warrior-queen. The Fir Bolg broke and routed pursued by their foe. They caught up with the Eochaid, the Fir Bolg King by the coastline and he was slain by the Morrigan.
The swift victory meant the new rulers and their people could invest in the country and they did. However, due to the Tuatha having a law that prevented Nuada being king on account of his severe injury a new king was chosen.
That king was Bres, a poor choice as it turned out.
He was half-fomorian and half-tuatha, the mix was not a good one, despite him being a youthful and seemingly charming ruler he possessed little abilty for kingship. Soon his mis-rule and constant bowing down to the Fomorian's saw extortionate amounts of 'tribute' pass into Fomorian hands.
Goods, precious resources and even children were sent to a dubious fate under Bres' order.
The Tuatha de Danann suffered for a few years under his yoke until finally an enlightened druid crafted a silver hand for the former king. Nuada was whole again and soon mustered his people into battle once more. This time against the Formorians.
Lugh was made Champion of the Tuatha and he used an artifact called the Spear of Lug to blind the giant Balor. With this the army of Tuatha defeated them in the Battle of Madura.
The newcomer's then made the Capital of Eiru at that time, Tara, their home and were said to of ruled wisely and peacefully from then onwards. Gifts and artifacts were abound in those days. One is even reputed to of been the stone of scone that the Scots covet.
A mystery school teaching the arts of the Tuatha Dannan was set up by Dannan Manananon on an Island that became known as The Isle of Mann.
After a fairly long and prosperous time, with adventures, story's and saga's galore.
The Druids, Fianna Fail and Bard's all were directly influenced by the Tuatha De Dannan. There is a legend of them creating a silver limb for one of their kings who had his original hacked off during the Battle of Madura. A form of the Elixur of Youth; The Cauldron of Dagda was also present, from this the legend of the Holy Grail stem's.
Finn McCool, Cucherlain, the Morrigan, Banshee and all manner of tale's were recorded orally from the Druids which was later written down by the Irish monks (encouraged by St Patrick).
The age of gods / demigods on earth was coming to a close and the Tuatha de Dannan knew it.
A new force for change was coming in the form of the Milesian's (thought to be the Celts).
The Tuatha De Dannan did what they could to keep the mortal ships at bay with contrary winds but their time was up. The Milesian's drew up for battle at Teltown. This time the Tuatha De Dannan were leaving though and drew up a great fog and vanished. Some said into the sky, other's into the earth or ether.
Although the Tuatha were gone physically, they left behind a great legacy that the Druids and kings continued. The Celts who arrived also continued this and the sacred knowledge was present in Scotland, Wales and England up until the time of the Roman invasions.
From 40 BC onwards the Roman's pushed back the Britons, many of whom retreated to Wales and Scotland and even Ireland.
At the Isle of Angelsey the Celts made their last stand...
"On the coastline, a line of warriors of the opposition was stationed, mainly made up of armed men, amongst them women, with their hair blowing in the wind, while they were carrying torches. Druids were among them, shouting terrifying spells, their hands raised towards the heavens, which scared our soldiers so much that their limbs became paralyzed. As a result, they remained stationary and were inquired. At the end of the battle, the Romans were victorious, and the holy oaks of the Druids were destroyed."
The brave last stand at Angelsey was the swan song for any Celtic resistance in Britain, although there was a further attempt that nearly succeeded during the Boudiccia Uprising.
The Druid's lived on in Eiru until they slowly assimilated into the Christian Church which St Patrick skillfully managed. It is to his credit that he encouraged the writing of the legends and history of the Tuatha De Dannan. Partly because he wanted to acknowledge the ancient race / age of those times and have a Christian / Celtic fusion between the two. After St Patrick died though the power of Rome tried to put a stop to that, although the whily Irish monks kept on scribbling and copying them anyway ;)
This is the legend of how he drove the snakes out of Eire into the sea. This is often interpretted as driving out the so-called Pagan way's of the Tuatha De Dannan with Christianity in it's stead.
However it could be an allegory of how the Tuatha De Dannan withdrew to sea following the show-down at Teltown but with St Patrick in place of the Milesians...
Annals of the Four Masters
Book of Billamote