The Milesians come from Galiza. Independent Irish and Galician traditions agree on this point.
The hypothesis of the Gaels coming from Galiza as in the Gaelic tradition can be read is here compared with the Galician tradition and same Celtic gaelic origin. Communication by sea between Galiza and Éire can be traced to prehistoric times. This confirm that the sea route Galiza-Éire was a reality in more recent historic times, after the 6th century b.C. when Galicia and Éire were already settled by gaelic Celtic tribes.
The names galego and Galiza came from the gaelic "old woman", more convenient the mother goddess Caillaech. In two altars in Sobreira, close to Porto, the name of the mother-goddess in its latinized form reads "Calaicia". (More on this topic, written in the modern Galician language can be read in chapter 1 of the book Galiza Celta)
When the Romans first come to Galiza, the historical Gallaecia, after crossing the river Douro, they found the first Celtic tribe: the worshipers of Caillaech, from where came the first Latin name for the area, "Cal-leac-ia", and the name of the people, the "Cal-laec-i". The people local particular celtic hard pronunciation rend it "Gal-leac-ia" and "gal-leg-o", ns of the mother goddess", and Galizafrom were come the actual name, Galiza or Galicia. So Galego means "the so "the beautiful land of the Mother-goddess" of the gaelic Celts.
The Roman general that defeated this Celtic tribe was given the surname of Decimo Junio Brutus the Galleacus (Calaicus). The Latin origin of the radical "gal-" could be traced from the early contacts between Latin and Celtic people in Central Europe. (The name of the present Polonaise town of Kalizs which gave origin to the similar name of Galicja came as well from the mother-goddess, Calleach). So the Greek "keltoi" become "gal", "gal-li" for the Romans. The names "gaels", "galego", "galos" have the very same origin.
The Celtic Gaels, speaking Gaelic, who are the people of the first invasion of Éire, came not from Spain, but from Galicia, from the other side of the bay, as we use to say.
Galiza is the only Celtic country left in the Iberian peninsula. The few tribes in Central Spain of mixed Celtiberian blood were completely annihilated by the Roman general Servius Sulpicius Galba in 151 b.C., who massacred the Celtiberians and mixed blood of Celts and Iberians after they had surrendered. For this massacre of children and women he was charged by the roman Senate with war crimes.
The tradition of both countries, Galiza and Éire, related with this sailing, the crossing of the Celtic sea from A Coruña to Cork, and over two thousand years apart, have a lot of surprising similar points.
Written tradition is no less wrong than oral tradition. Also, putting in write something doesn't make it more true. Tradition, written and oral, play an important role helping to interpretate and to build hypothesis to understand history. Coherency of history can't be neglected.
Graffiti on the rocks was the game some three or four thousand years ago. We are talking about petroglyphs.
Petroglyphs such as round motifs: circle with a cross inside (Celtic cross), circles with a dot in the center, circles with a small concentric circle inside, circles with a line showing the center or the spiral showing its center are very common on the Atlantic side of Europe and exclusively of the seashore lands. They are most important for its number and similarity in Galiza and Éire, but they are found from Brittany until Scotland. Another such typical seaboard Petrography are arms designs. They are too found in the Atlantic Europe area, in the presently known as Celtic Lands. Because they are difficult to date, for obvious reasons, we can assert a certain date, but they are old enough to put all b.C. and many centuries before. We can also find some exclusive type of bronze axes for Galiza and Éire, along with lots of archeological similarities between both countries.
The point is that there is not other explanation than the people around the Celtic sea, this triangle extending from the Galician Fisterra to the Breizh Finistère to the Kernow Lands End and to South Éire, have had contacts by sea in pre-historic times.
A sail from Galicia to Brittany could be 2 to 3 days away, from Galiza to Wales 2 to 4 days and from Galiza to Éire can take from 3 to 5 days. And shorter in the all the others cases. If pre-historic people could do such navigation, then more recent, historical people as the Celts, could do it also.
The more traditional way of navigation two thousand years ago could be coastal navigation, for it seems to be the simplest way. It is well know that Mediterranean people as well the Vikings used coastal navigation for they salings. There was another kind of navigation which still is in use today and fits better our purposes: following the predominant winds.
For the area Galicia-Éire, a 480 miles sail or less, both countries are in the same meridian, about 6 degrees west, the navigation could be the easy north-south. The predominant winds are from the west, a reach sail; good weather, anticyclone for the area, the winds are from the NW, a depression in the area the winds are from the SW. To navigate North-South (Éire-Galiza) or South-North (Galiza-Éire) will be the easy way because with the western predominant winds we could have a reach or tree quarters back. Also, not need for a compass, the stars can do it, this is south-north navigation. Galiza and Éire are across the bay.
The first historical people of Galicia were gaelic Celts, and this country was heavily settled by Celts before the VI century b.C. Communication by sea, between the different Celtic countries of the Atlantic land-ends was a reality as archeology has proven. There has been found traces of brythonic Celts in Galiza from this period ("Briteiros castrodun") and we know from History that brythonic Celts came to Galiza lately in the 5th and 6th centuries a.C. (like bishop Maeloc); they were the same people that sailed to Armorica from saxon England to create Breizh (Brittany) and they knew well the other Celtic countries with which they have many contacts. They do not sailed to North Spain (Iberian countries, such as Astures or Vascones) or Southwest of France (Aquitanians, also Iberians), but they come to Armorica (Breizh) and Galiza, both Celtic countries. So this is a evidence of the sea communication between the different Celtic countries b.C.
What it is well know from history too is that before the roman colonization at the end of the first century b.C. (3rd century in Galicia) there was a strong connection by sea, across the Celtic sea between the Celts of the many land ends: Éire, Galiza, Wales, Scotland... Descriptions and pictures of the leather boats are well known.
Galician fishermen have being fishing and sailing in the Celtic sea from centuries, on the "Gran Sol" (i.e. the Irish Box). On the sea, the best routes are determined by the predominant weather conditions. This route is well established. The Galicians have born to sail and the North-Atlantic seas were also part of their own home from centuries.
Legends and myths play an important role in every Celtic culture. The Celts didn't have any writing, simply did not write, for all the knowledge was transmited in oral form. All we know about their knowledge came through other people who interpreted it with the filter of their own knowledge, most them fiercest enemies.
We call most of the Celtic oral tradition myth or legends because they have intermixed natural and supernatural things, possible and impossible, real and imaginary, true and false... So we just don't trust people that said true and false, because we do not believe in their purpose, they try to mix-up. For the Celts this was not their intention, what to us appears as supernatural, impossible, imaginary... was part of their reality, as is today is in many Celtic countries. Water, rocks, nature is supernatural, all have specific powers, all are part of the real life. In Galiza today this is so strong that you´ll finish believing yourself. People go to specific places, most today with Christian names and Saints as central figures, to cure of specific ailments: Serans for the warts, Ribacarte to full dead, Ortigueira you´ll go live or dead, the night of the solstice (Briga) to fall pregnant, the water of the river, the Laxe... they are old Celtic recipes and they do work indeed! Any Galician will confirm it to you.
We should understand too that most of these "myths" were only written in very recent times (many centuries after and by religious people) compared with the time of occurrence. This is the case for the Book of Invasions of Éire (Leabhar Gabhala), which was done by people who had a very important knowledge of the Bible and its related myths, probably the only people that could write. So they incorporated a lot of Christian and biblical myths to Celtic ones.
But it is yet possible to extract some information from myths. These tales were written many centuries after, in a period when Christianity was so powerful and have so much influence over all aspects of life that this is what is most noticed in these relates. The Bible was the Book, the most important around to whom everything is referred and measured. The important things in history and knowledge were to be found in the Bible, its people, its lands. The Mediterranean world, Hebrews, Egyptians... had the most importance, references to this biblical world, they were important, they established the rule, the measure:
(Chuck Larkin referring to a 19th century written and oral tradition of Scotland).
"We sailed the river Nile, we sailed across the sea, and as Cailleach's navigator, we sailed the Iberian coast to the river Munda. And with our swords and shields we settled on the coast of what you call Portugal. Our life was good. Scota's sons and daughters sailed to Ireland and Scota's grandchildren carried their arms and shields into northern Albyn where they fought the Grog-Magog and Termagol and in honor of their Queen and grandmother they called themselves Scots and their new land Scotland. I and my wife Queen Scota and my grandchildren and our Clan had arrived in the land from the dream time." --
I want to notice that in North Galicia there is a river called Mondego very close from another called Mendo, and this is exactly the area were the Galician tradition places the sail of Ith, son of the Galician Celtic king Breogán, to Éire, call in the Galician tradition "the green-island"! Also Portugal is a recent name and was formed by the scission of the old Gallaecia in two kingdoms: South of Gallaecia was the Lusitania, the main part of today Portugal, where a river called Mondego is also located, on the border of the historical Galicia.
The Greeks gave the name of Esperia and the Romans Hispania from the cartaginese name of the country to the South and Mediterranean sides of the Iberian Peninsula, first till the Ebro river, and lately for the whole area with the only exclusion of the West side, i.e. Galiza and Lusitania that are naturally separated by mountain chains (the border Spain-Portugal is the most stable and oldest border of all Europe). Lately, for roman purposes only, they extended the name to the whole peninsula. Moreover, the name "Easpain" which was only applied to the mass of land on the East side of the Iberian peninsula, was applied by Irish monks to the whole peninsula. But to the south of Éire lies the only land heavily settled by Celts, that today is called Galiza to remember its first historical settlements, the gaelic Celts, from where the Gaels come.
So if we take off all reference to the Mediterranean world, all that comes from the biblical myth, there is certainly not much left but, even if corrupt in time, this something that is left, could be compared with other sources.
Without making any conclusion I would like to refer you to the book of invasions of Éire, who is the oldest in Celtic mythology to my knowledge.
I retain that Scotta marry Mil (referred also as Mile, Milesius, Golamh...). Both came from the Otherworld, the land of dead and they have sons: Ir, Bregon, Arannan... The sons and the grand-sons sailed to Éire. This is the invasion of the gaelic Celts, the Gaels. Ith the son of Bregon was born in the other land were his father had built a big tower.
Now, in accord with present Galicia's tradition, the Galician Breogán had built a big lighthouse in Brigantia (today know as A Coruña, and rebuild by Romans and more recent times exactly in the same place, still a landmark looking to the Celtic sea and remembering every one of this sail more that two thousands years ago, the sailing by Ith from Galiza to Éire), he and his sons have sailed in a leather boat, a trip of five days, to a green land at the north, just across the sea they use to sail. (As we have seen, five days is about the time for a sail between Galiza and Éire). Avenues talking of the "galegos", the Galicians, made a full descriptions of its leather boats, picture on rocks of the time confirm.
Now the hypothesis of considering the Otherworld of the book of invasion as Galiza and the green land of the galegos as Éire. The hypothesis of identifying Gaels = Galegos is very appealling.
In the first hand, with a little of knowledge about navigation, it's easy to realize that a sail from Galiza to Éire and back is a very easy sail in the prevailing wind conditions, a natural way to sail. For a sail of less that 500 miles in the direction south-north and reverse, is of simple navigation even at that old times, specially if you know that the prevailing winds are some times SW and others NW. This would make a perfect navigation and easy land fall in both ways for a sailing craft.
Two, identifying Galiza with the Otherworld, the land of dead, the land of Mile and Scota is not difficult in accord to Galicia's references.
Even today, the west coast of Galiza has the name "Costa da Morte" (Coast of Death). But the main reason I want to advance is the deep cult to death, still very alive in the whole Galician country and specially in the north-west coast. Celtic traditions, older than more than 2,000 years, are still alive (though now christianized): the living people play death to escape from dead. Many villages conserve this particular tradition: A Póvoa do Caramiñal, Rivacarte... where alives fools deads. The death are always present on the streets at night, being named the "ánimas" or "a estadea" in Galician (from the all Gaelic "eistedd" and "ann" meaning, i.e., "gathering of dead", and this is exactly what for Galician means). You can hear them in the dark nights of winter as they pull their chains and they mock you... the Halloween night you see them everywhere. And this is true! You can see the dead, ask any Galician. Because the Catholic religion forbidden to believe in not Christian supernatural spirits, Galicians use to say: "crér non creo, pero habelas hainas" [I just don't believe, but they do exist indeed].
Many aspects of life in Galiza reveal this deep identification with the world of the dead. The OtherWorld of the Gaels, the people that emigrated from there, was Galiza the land they know well (the OtherWorld = the OtherLand = Galiza) and too the land where the cult to the dead (Land of Dead = Land the cult to death) was so deeply enrooted, as still today, the land of the dead, as today the West coast of Galiza carry this name.
For the Galicians, Breogán is the founding father of the Galician Celtic nation and they recognized as such in the present Galician national anthem where they sing to Breogán.
The lighthouse in Brigantia (A Coruña) is still there, in the same place where Ith was born (know today as "the Hércules Tower", a name given from a bad interpretation in the last century when the Spanish idea of the supremacy of the Mediterranean world over the Atlantic world was dogma). It was is this tower, the oldest lighthouse emplacement in the Atlantic world, first build by Breogán and rebuilt many times after, always in the same place.
Next, identifying Éire's Bregon with Galiza's Breogán is not really difficult if we know from Éire's invasion book, that the son of Bregon, Ith, was born in the Otherworld and has lived there in a tower build by his father (the lighthouse of Art-o-briga, Galician Gaelic for "the bear of the goddess Brig", the town of A Coruña, still today in the same place.
It is clear that the Gaels came from Galiza, where the same people are still called "galegos". That Mil and Scotta are born there and that this two names become two Irish names. From Scotta came the name of a people that later come to Alba and... history follows. Scota is the wife of Mil. This name, Mil, means, or late is used to mean a "warrior". There is even today in Galiza lots of names of villages who use the old gaelic word "mil = warrior", such as Ardemil (Gaelic for high-warrior), Belmil (warrior of Bel), Antemil, and so on.
So, if some invasions of Éire came from the South, they came from Galiza. Galiza and Éire share many traditions, the same Gaelic Celtic heritage (see, in Galician, Galiza Celta chapter 5) and "they are just across the bay". You want a better proof, take an old Gaelic dictionary (the old Gaelic roots better) and you will be happy surprised to translate most of the old Galician place-names. In the Galician toponimy are written the oldest aspects of the Celtic culture in Europe. Galiza, this great forgotten Celtic land.