Traces of life found in the south of Ille-et-Vilaine in Saint-Malo de Phily (North Brittany) provide evidence of human presence 600,000 years ago. Around 10,000 BC, a community using flint existed in Saint-Michel Chef-Chef (Loire-Atlantique, 40 km from Nantes), and other traces enable us to know that groups living on the coast in Finistère and Ille-et Vilaine had the same activities. In Plouézoc'h, a cairn (artificial pile of stones) (de Barnenez) was erected in 4,800 BC.
The first historian to look at this thorny subject was Dom Taillandier in the 18th century.
You only have to look at a map to follow the implantation of the Bretons "invaders" in Armorica. The dominance of Bretons over the Gauls can be seen in village and place names, with prefixes plou, tre or lan.
The original map, engraved in its graduated frame, was dedicated in 1771 to the Duke of Duras (1715-1789), noble and high ranking officer, who was responsible for order in Brittany. It was reused by Breton députés (elected politicians) to trace in colour the new administrative divisions decreed by the Constituent Assembly between December 1789 and February 1790: five départments with geographical names (Finistère, Côtes-du-Nord, Morbihan, Ille-et-Vilaine, Loire-Inférieure) and forty-five districts, defined around important towns, overlapping with the former province's dioceses. Only a slight dispute at the extreme south-east required a brief negotiation - "We must follow the trace indicated by the black line". On February 26, 1790, with rapidity and enthusiasm, the députés endorsed the new face of Brittany from Paris - "we approve the current map, with the duplicate serving as minutes, for the division of the province of Brittany into 5 départements and 45 districts, in Paris, on February 26, 1790".
The current Brittany region does not correspond to the historic Duchy of Brittany which was attached to the Kingdom of France in 1532, as Nantes and Loire-Atlantique are missing. However, the Breton identity is historically anchored there.
In August 1941, under the Vichy regime, regional prefectures were created in the occupied territories, one of these being managed from Rennes and made up of 4 départements. The pays de la Loire was attached to the region managed from Angers, but the same year, a 5 département Brittany was created.
In 1956, the French Government of Edgar Faure defined the regions, with Brittany only including four départements; the Loire inférieure (now Loire Atlantique) rejoined the pays de Loire (region with no historical signification). However, many would like to see the return to a Brittany with 5 départements.
Read more about Brittany history here
(Source Histoire de la Bretagne (History of Brittany) by Joël Cornette, Editions Points 2008)