It is my understanding that most of the tales of Rome's founding and the establishment of Republic are about equal parts fact and fiction.  It sounds better to have semi-mythical origins, especially when you are busy subjugating your neighbors.  It makes success easier to stomach for the conquered if they think that it was ordained and makes the conquerors feel that they are just enacting the God's plan.  We often forget the pivotal role that religion and superstition played in Greek and Roman times.  This is especially so given the advances in science and philosophy they made.  Mythic origins fed into the Roman perception that they were doing the right thing.

The Romans were an exceedingly pragmatic people.  They came up with logic for some of their wars that would leave the best sophist's head spinning.  Some of their logic sounds suspiciously like what was used to get us into Iraq.  The important thing about Roman logic is not what it means to us though, it is that it satisfied the Roman need to be seen as only acting defensively, even if they were the only ones that thought so.  A kind of solipsism, if you will.  In the end, a people only really has to justify things to themselves, especially if they win, as the Romans did.  the very fact of their success seemed to justify their actions by showing that they were favored by the gods.

That may sound about right.  I had read about them as being somewhere near the Scythians, which was actually western Asia.  The Celts must therefore have been nomadic for many centuries.

The Celts certainly migrated.  I think they originally came out of the limitless steppes of Russia like so many other peoples.  There are many Celtic sites in southern Germany as well.  They just eventually ended up in Ireland after being driven from the continent by subsequent waves of migration.

The Celts did certainly migrate but they didn't end up in Ireland as a consequence of different waves of migrations. When we talk about these migrations, it's about the Indo-European people who might have lived in an area located between the Black sea and the Caspian sea. Among the different hypothesis (because no primary sources can confirm it so far) concerning these Indo-Europeans, few things about their culture can be determined with confidence according the reconstruction of their language from current Indo-European languages (from Irish to Sanskrit):- Around 3000 BC some of the people who spoke Indo-European language began to travel away from their place. - Some of them went west toward the Atlantic ocean and these are now known as the Celts, and they speak the Celtic languages: Gaelic, Welsh, Breton and Cornish. - Another group went east toward China, and these are now known as the Tocharians, though they speak Chinese now.  - A little later, others travelled over the Black Sea toward the Mediterranean or south to Western Asia.  Some of them settled in Italy, where Indo-European became Latin.  Others settled in Greece, where Indo-European became Greek.  Some went north, where Indo-European turned into German, Danish, Swedish, and English. - The people who stayed more or less where they were in the Balkans and Russia began to speak the Slavic and Baltic languages: Russian, Polish, Lithuanian. - Some went to Western Asia, where they spoke Hittite and Persian, and some went all the way south to India, where they spoke Sanskrit In India, the Indo-Europeans are usually called the Aryans. Scythians are among these people.- About the Celts, the historical Celts were diverse groups of tribal societies in Iron Age Europe. Proto-Celtic culture formed in the Early Iron Age in Central Europe (Hallstatt period, named for the site in present-day Austria). By the later Iron Age (La T?ne period), Celts had expanded over wide range of lands: as far west as Ireland and the Iberian Peninsula, as far east as Galatia (central Anatolia), and as far north as Scotland.