I hope I'm not very late. I would like to clarify a matter (something

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There is an opinion that the Celts spoke a common Celtic language. Celtic scholars have supposed this common Celtic may have been spoken just before the start of the first millennium BC. during the Urnfield/Hallstatt eras. Soon after, five(?) distinct dialects emerged which may be subdivided as follows:
Hispano-Celtic (now obsolete)
Gallic (now obsolete)
Lepontic (now obsolete). Lepontic was a speech-form spoken in Northern Italy around the time of Christ, attested by a handful of short inscriptions in a form of the Etruscan alphabet.
Goidelic or ‘Q-Celtic' (which includes Irish, Scots Gaelic, and Manx)
Brythonic or ‘P-Celtic' (which includes Welsh, Breton, and Cornish)
Unfortunately, since no version of Hispano-Celtic, Gallic, or Lepontic has survived, we do not know whether they were distinct dialects, or whether they also were part of the P-Celtic and Q-Celtic variety. Pictish seems to have included a large element of Gallic or Welsh, but of an early type no longer identical with the Welsh of today.
Goidelic is said to be an older form than Brythonic, which may have developed from Goidelic at a later stage. Brythonic simplified itself in its case endings and in changes of gender. The major difference between the two dialects, is the substitution of P for Q in Brythonic, hence the terms P-Celtic and Q-Celtic. This is based on the Indo-European sound "qu(kw)". The sound in Goidelic later became represented by "c" (always hard), which in Bythonic it was replaced by "p". An example of this can be seen in the word for son. In Goidelic it is "mac", in Bythonic it is "map" or "mab".
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From what I’ve read recently, Ireland was a major player in the Atlantic zone before 600 BC and then was relegated to a forgotten backwater between 600-200 BC (hmmm, about when the Hallstatt & La Tène elites were flexing their muscles...). Since they have one of the older Celtic language forms, it is supposed to have been in place at least between 1200-600BC.
The Hallstatt era is divided into four phases: A, B, C, and D, by modern day archaeologists. Approximately, Hallstatt A and B correspond to the late Bronze Age, c. 1200-800 BC; Hallstatt C refers to the very early Iron age, c. 800-600 BC; and Hallstatt D ranges from c. 600-500 BC. During Hallstatt A and B there is an apparent lack of large scale political organization. Until the eighth century, the known settlements suggest no more than petty chiefdoms. It is during the Hallstatt C period that we start to see fortified settlements on hilltops north of the Alps with greater frequency. Consequently, many burial mounds mark the graves of the rising noble classes, who no doubt had the hillforts built. Increased trade volumes seem to have contributed to the rise of these nobles. In the last phase, Hallstatt D, the richest graves are more concentrated in the west than previously. Resulting, seemly from the wishing to be closer to trade routes to the newly founded Greek colony of Massalia (Marseilles), near the mouth of the Rhône. Reaching the Greek world via Massalia, stories about the 'barbarian' chiefdoms were in all likelihood one of the earliest sources for tales of the people called Keltoi.
The fifth century BC began with a sudden extinction of the rich chiefdoms of the Hallstatt D. Hillforts all over Central Europe were abandoned, and rich burials ceased. At about the same time, wealthy warrior societies were developing, mostly to the north of the old Hallstatt centers. Almost certainly Celtic speakers, these peoples founded a unique culture and developed an artistic style unlike anything previously seen. This then is the developement of the
La Tène culture.Whereas the Hallstatt culture probably consisted of many different peoples and language groups, the La Tène culture can truly be termed "Celtic". The La Tène culture evolved during the fifth century BC in part of the Hallstatt area. There are several reasons for distniguishing archaeologically between the Hallstatt and La Tène cultures. One most important and distictively different feature of the La Tène culture is the unique art-style, usually represented in their metal-work. This style most likely developed between the Meuse, Neckar, and Main, and had spread quite rapidly. The era in which it flourished begins around 500 BC. and ends, on the European continent at least, around 50 BC.
La Tène Culture lifts the Celts from being just another of the many European tribal peoples. La Tène truly establishes the Celts as a real 'civilization'. La Tène Culture generated some of the ancient world's most stunningly beautiful pieces of decorative art. The use of animals, plants, and spiral patterns in the art eventually epitomized and perpetuated the legend of the Celts.
La Tène society seems to have risen to prominence through trade with the Mediterranean, with the Greeks and Etruscans, and later the Romans. La Tène Culture finds the Celts amonst wealth and glory and expression. In general, the technological level of the La Tène Celts, with very few exceptions, was equal to, and in some cases surpassed. that of the Romans.
It was inevitable, however, that in any conflict between the Celts and Romans, the superior powers of organization, discipline, and orderliness of the Roman culture were bound to overcome the passionate and undisciplined Celts. But before the Romans were able to conquer the greater part of Celtic-dominated areas of continental Europe, the Celts during the La Tène period were to achieve their most widespread expansion. They spread into and beyond those areas previously held by the Urnfield and Hallstatt cultures. They forced their way into Greek and Roman history by sacking Rome in 390 BC and Delphi around 279 BC.
With the La Tène Culture, the Celts came of age and marked a major cultural presence in Europe. Through La Tène, European peoples saw them as important, powerful, and something to be feared. Their spread across the continent and their impressive pressence, made them a force to be reckoned with. From Germany and Eastern Europe they spread southward into the balkans and Italy, and westward into France and Iberia. Before the La Tène culture of the Celts was finally destroyed by Roman conquest and culture, some of its elements had travelled beyond the continent into the British Isles. Ireland remained (at least no evidence suggests) untouched by the Romans.
With the La Tène culture, the Celts had given themselves definition, acquired a considerable presence, and earned respect from all the peoples of Europe at that time.
Sorry, I would like to give a link but couldn't find the site. I used thoughts of Michael Wangbickler in my work a time ago.