The Germans are coming.

Cauci 

The Cauci (Καῦκοι) were a people of early Ireland, uniquely documented in Ptolemy's 2nd-century Geography, which locates them roughly in the region of modern County Dublin and County Wicklow.[1] From the early 19th century, comparative linguists, notably Lorenz Diefenbach, identified the Cauci with the Germanic Chauci of the Low Countries and north-western Germany, a parallel already drawn by earlier antiquarian scholarship.[2] Proponents of this view also pointed to the fact that the Manapii (Μανάπιοι), who in Ptolemy's map border the Cauci to the south, likewise bear a name that is almost identical to that of another continental tribe, the Belgic Menapii in north-eastern Gaul. This correspondence appeared to testify to population movements between the two regions. The linguistic aspect of this hypothesis was most recently (1917) developed by Julius Pokorny,[3] although the Cauci-Chauci association is not universally accepted.[4] This early scholarship also drew attention to apparent parallels among Celtic or Celticized peoples of the Iberian peninsula, specifically a leader of the Lusitani named Kaukainos (Καυκαῖνος), and a city called Kauka (Καύκα) (modern Coca), inhabited by Kaukaioi (Καυκαῖοι), among the Vaccaei, a prominent Celtiberian people.[5] With regard to possible descendants of the Irish Cauci, Pokorny and Ó Briain[6] respectively favoured the obscure medieval septs of Uí Cuaich and Cuachraige, though in neither case has a connection been demonstrated.

 

Chauci

 The Chauci (German: Chauken, and identical or similar in other regional modern languages) were an ancient Germanic tribe living in the low-lying region between the Rivers Ems and Elbe, on both sides of the Weser and ranging as far inland as the upper Weser. Along the coast they lived on artificial hills called terpen, built high enough to remain dry during the highest tide. A dense population of Chauci lived further inland, and they are presumed to have lived in a manner similar to the lives of the other Germanic peoples of the region.
Their ultimate origins are not well understood. In the Germanic pre-Migration Period (i.e., before c. 300 AD) the Chauci and the related Frisians, Saxons, and Angles inhabited the Continental European coast from the Zuyder Zee to south Jutland.[1] All of these peoples shared a common material culture, and so cannot be defined archaeologically.[2] The Chauci originally centered on the Weser and Elbe, but in c. AD 58 they expanded westward to the River Ems by expelling the neighboring Ampsivarii,[3][4] whereby they gained a border with the Frisians to the west. The Romans referred to the Chauci living between the Weser and Elbe as the 'Greater Chauci' and those living between the Ems and Weser as the 'Lesser Chauci'.[5]
The Chauci entered the historical record in descriptions of them by classical Roman sources late in the 1st century BC in the context of Roman military campaigns and sea raiding. For the next 200 years the Chauci provided Roman auxiliaries through treaty obligations, but they also appear in their own right in concert with other Germanic tribes, opposing the Romans. Accounts of wars therefore mention the Chauci on both sides of the conflict, though the actions of troops under treaty obligation were separate from the policies of the tribe.
The Chauci lost their separate identity in the 3rd century when they merged with the Saxons,[6] after which time they were considered to be Saxons. The circumstances of the merger are an unsettled issue of scholarly research.

So this is why we can’t have these road builder with the same name be the same people. Because that would mean that Germanic tribes inhabited East Ireland in the 2. Century. What would that do to the story of “Celtic Ireland”?
But that is surely a coincidence. Maybe they just have similar names and are completely different people? Let’s see how far we can stretch this coincidence:

If you look at Ptolemy’s map of Ireland, you see that south from Cauci, you find these tribes: Menapii, Coriodni, Brigantes, Vodiae. 

Do we find Menapii anywhere else? We do, right next and below the Chauci in the Rhine region.

The Menapii were a Belgic tribe of northern Gaul in pre-Roman and Roman times. According to descriptions in such authors as Strabo, Caesar, Pliny the Elder and Ptolemy their territory had stretched northwards to the mouth of the Rhine in the north, but more lastingly it stretched along the west of the Schelde. In later geographical terms this territory corresponds roughly to the modern coast of Flanders, the Belgian provinces of Oost and West Vlaanderen. It also extended into neighboring France and the river deltas of the southern Netherlands. 

Now interestingly enough they are a “Belgic” tribe. So we have a Belgic and Germanic people living in two places next to each other. This opens a big question again (as I am not the first to open it) :

Was there a difference between Belgic (Celtic) tribes and Germanic tribes, or are the Germans just Celts that Romans did not conquer?
 
In Ireland, just under the Manapii tribe you find Coriondi, who we also find in England and according to names study probably in Gaul as well, and I say probably next to Menapii.

The Coriondi (Κοριονδοί) were a people of early Ireland, referred to in Ptolemy's 2nd century Geography as living in southern Leinster.[1]MacNeill identifies a later Irish group, the Coraind, in the Boyne valley, who may be the same people.[2] Other possibly related names include the Corcu Cuirnd,[2] Cuirennrige and Dál Cuirind in early medieval Ireland, and in Britain, the Corionototae, known from an inscription inHexham, Northumberland, and Corinion, the Brythonic name for Cirencester, Gloucestershire.[1] The element *corio- also occurs in Gaulish personal and tribal names, usually taken to mean an army or troop of warriors [3]

Under Coriondi we find Brigantes, who are also found in England, and in the Alps.

The Brigantes were a Celtic tribe who in pre-Roman times controlled the largest section of what would become Northern England, and a significant part of the Midlands. Their kingdom is sometimes called Brigantia, and it was centred in what was later known as Yorkshire. Ptolemy lists the Brigantes also as a tribe in Ireland, where they could be found around Wexford, Kilkenny and Waterford[1] while another probably Celtic tribe named Brigantii is mentioned by Strabo as a sub-tribe of the Vindelici in the region of the Alps.[2]
Within Great Britain, the territory which the Brigantes inhabited was bordered by that of four other Celtic tribes: the Carvetii (to whom they may have been related) in the North-West, the Parisii to the east and, to the south, the Corieltauvi and the Cornovii. To the North was the territory of the Votadini, which straddled the present day border between England and Scotland.

The name Brigantes (Βρίγαντες) is cognate to that of the goddess Brigantia. The name is from a root meaning "high, elevated", and it is unclear whether settlements called Brigantium were so named as "high ones" in a metaphorical sense of nobility, or literally as "highlanders", referring to the Pennines, or inhabitants of physically elevated fortifications. (IEW, s.v. "bhereg'h-").
In modern Welsh the word braint means 'privilege, prestige' and comes from the same root brigantjā. Other cognates from the modern Celtic languages are: Welsh brenin 'king' (< *brigantīnos); Welsh/Cornish/Breton bri 'prestige, reputation, honour, dignity', Scottish Gaelic brìgh 'pith, power', Irish brí 'energy, significance', Manx bree 'power, energy' (all < *brīg-/brigj-); and Welsh/Cornish/Breton bre 'hill' (< *brigā). The name Bridget from Old Irish Brigit (Modern Irish Bríd) also comes from Brigantja, as does the English river name Brent.
There are several ancient settlements named Brigantium around Europe, such as Berganza in Alava (Spain), Betanzos and Bergondo in Galicia (Spain), Bragança in Portugal and Briançon,[3][4] Brigetio on the border of Slovakia and Hungary,[5][6] Brigobanne situated on the Breg river and near the Brigach river in south Germany (pre-Roman Vindelicia[7])[8] and Bregenz in the Alps.
The Old Italian word brigante, whence English and French brigand and brigade, occurs in medieval Latin in the 14th century in the forms brigancii, brigantii, brigantini, brigantes (OED). Although an ultimate Celtic origin for the word is possible, any connection of the Italian term to the Celtic ethnonym seems unlikely since the Brigantes had not played any significant role in Italy and had disappeared as a people for some thousand years by the time the word is attested.

Under Brigantes we find Vodiae or Vodii or Udiae: 
 

What we see is that we have the same Celto-Belgo-Germanic people settling one next to the other in:
1. South Baltic area, the same areas from which Ango-Saxons, and later Dano-Slavic Vikings, would later invade England.
2. North England, the same area that Ango-Saxons, and later Dano-Slavic Vikings, would later invade and settle in England
3. East Ireland, the same area Dano-Slavic Vikings, would later invade and settle in Ireland.

But there are not supposed to have been any Germanic or Ango-Saxon tribes in Ireland. Yet the territory of county Wexford, settled by Menapii is in Gaelic called: “Loch Garman”. 

Wiki says this about the name Loch Garman:

Wexford lies on the south side of Wexford Harbour, the estuary of the River Slaney. According to a local legend, the town got its Irish name, Loch Garman, from a young man named Garman Garbh who was drowned on the mudflats at the mouth of the River Slaney by flood waters released by an enchantress. The resulting loch or lough was thus named, Loch Garman.

However it is a lot more plausible that the Gaels called the teritory by the name of its inhabitants, the Lock of Garmans (Germans). 19th century English historians thought so. 

Ptolemy calls Wexford town by its real name Menappia, the town of Menapii.

Quite interesting are the Vodii as well. In modern Gaelic Irish the word for water is “uisce” pronounced “ishka”. However I believe that once there was another word for water, which has central European origin: “bwo” or “bwa” or “bwoa”. This word is the route of the word for water (English), wasser (Serman), and (Voda) Slavic. I believe that it is hidden in the following Irish word:

bá (bvao) – Bay, great expense of water, flooding, drowning, immersion, quenching of thirst

The area inhabited by the Vodii, whose name in Serbian would mean water people, is today called Waterford. 

There is also in Irish annals a story about an Irish prince of Leinster who was exiled to continental Europe and, befriending the foreign king, he returned with an army of Laigin, the "long spears" which, in Gaelic, was at the origin of the province name of Leinster:

Early Irish historical traditions credited the founding of the Laigin to the legendary High King Labraid Loingsech. His grandfather,Lóegaire Lorc, had been overthrown by his own brother, Cobthach Cóel Breg, and Labraid forced into exile. After a period of military service on the continent, Labraid returned to Ireland at the head of an army, known as Laigin after the broad blue-grey iron spearheads (láigne) they carried. The Lebor Gabála Érenn dates Labraid's accession to 300 BC.[3][4][5] Modern historians suggest, on the basis of these traditions and related placenames, that the Laigin were a group of invaders from Gaul or Britain, who arrived no later than the 6th century BC, and were later incorporated into the medieval genealogical scheme which made all the ruling groups of early Ireland descend from Míl Espáine. Placenames also suggest they once had a presence in north Munster and in Connacht.[6]

Now what is the name for a spear in in old Germanic languages? The word for spear in Germanic languages is “gar”. Which would mean that Garman is a Gar man which means a Spear man. So back to Lock Garman again, and this time in the country of the spear men we have a town of the spear men.

gar: From Middle English gar, gare, gere, gore, from Old English gār (“spear, dart, javelin, shaft, arrow, weapon, arms”), from Proto-Germanic *gaizaz (“spear, pike, javelin”), from Proto-Indo-European *ǵʰayso- (“pointed stick, spear”), from Proto-Indo-European *ǵʰey- (“to drive, move, fling”). Cognate with West Frisian gear, Dutch geer (“pointed weapon, spear”), German Ger (“spear”), Norwegian geir (“spear”), Icelandic geir (“spear”). Related to gore.
Old Irish has gae "spear"

Which leads me to an inevitable question: Does German actually just mean a "spear man"? And are Germanic tribes just tribes of people armed with Gars, Spears???

If Saxon or Sekson is a sek man, a man with saex, saek, long blade, then German or Garman could well be a gar man, a man with a spear? What this brings us to is that neither of the two main “national” or “ethnic” names for Germanic people have nothing to do with race. These names distinguish people by the type of weapon they use. So who were Gar-men and Sek-men ethnically? Maybe we will be able to answer this and maybe not, but it’s definitely an interesting question.