Revolution in Brittany did not happen due to a radical change of population, but by slow immigration and exchange of skills. Neolithic Brittany is characterised by important megalithic production and sites such as Quelfénnec, it is sometimes designated as the "core area" of megalithic culture. The oldest monuments, cairns, were followed by princely tombs and stone rows. The Morbihan département, on the southern coast, comprises a large share of these structures, including the Carnac stones and the Broken Menhir of Er Grah in the Locmariaquer megaliths, the largest single stone erected by Neolithic people. Gallic era During the protohistorical period, Brittany was inhabited by five Celtic tribes: The Curiosolitae, who lived around the present town of Corseul. Their territory encompassed parts of Côtes-d'Armor, Ille-et-Vilaine and Morbihan départements. The Namnetes, who lived in the current Loire-Atlantique département (in today's administrative région of Pays de la Loire), north of the Loire. They gave their name to the city of Nantes. The south bank of the river was occupied by an allied tribe, the Ambilatres, whose existence and territory remain unsure. The Osismii, who lived in the western part of Brittany. Their territory comprised the Finistère département and the western extremity of Côtes-d'Armor and Morbihan. The Redones (or Rhedones), who lived in the eastern part of the Ille-et-Vilaine département. They gave their name to the city of Rennes (Roazhon in Breton language, in the center of the département) and to the town of Redon (in the south of the département, bordering the département of Loire-Atlantique in the administrative région of Pays de la Loire, where its suburb town of Saint-Nicolas-de-Redon is located; however the city of Redon was founded around AD 832 under the initial name of Riedones, long after the Redones people were assimilated to Bretons; the cultural link between Riedones and the former Redones people is highly probable but difficult to recover and the name of Riedones may have been written from a local usage preserving the name of the former people in the vernacular oral language from a reading of an ancient Greek orthography). The Veneti, who lived in the present Morbihan département and gave their name to the city of Vannes. Despite confusion by the classical scholar Strabo, they were unrelated to the Adriatic Veneti. Those people had strong economic ties to the Insular Celts, especially for the tin trade . Several tribes also belonged to an "Armorican confederation"