Of Brittany before the coming of the Romans we have no exact knowledge. The only traces left by the primitive populations are the megalithic monuments (dolmens, menhirs and cromlechs), which remain to this day in great numbers (see Stone Monuments). In 56 B.C. the Romans destroyed the fleet of the Veneti, and in 52 the inhabitants of Armorica took part in the great insurrection of the Gauls against Caesar, but were subdued finally by him in 51. Roman civilization was then established for several centuries in Brittany.
In the 5th century numbers of the Celtic inhabitants of Britain, flying from the Angles and Saxons, emigrated to Armorica, and populated a great part of the peninsula. Converted to Christianity, the new-comers founded monasteries which helped to clear the land, the greater part of which was barren and wild. The Celtic immigrants formed the counties of Vannes, Cornouaille, Léon and Domnonée. A powerful aristocracy was constituted, which owned estates and had them cultivated by serfs or villeins. The Celts sustained a long struggle against the Frankish kings, who only nominally occupied Brittany. Louis the Pious placed a native chief Nomenoë at the head of Brittany. There was then a fairly long period of peace; but Nomenoë rebelled against Charles the Bald, defeated him, and forced him, in 846, to recognize the independence of Brittany. The end of the 9th century and the beginning of the 10th were remarkable for the invasions of the Northmen. On several occasions they were driven back - by Salomon (d. 874) and afterwards by Alain, count of Vannes (d. 907) - but it was Alain Barbetorte (d. 952) who gained the decisive victory over them.
In the second half of the 10th century and in the 11th century the counts of Rennes were predominant in Brittany. Geoffrey, son of Conan, took the title of duke of Brittany in 992. Conan II., Geoffrey's grandson, threatened by the revolts of the nobles, was attacked also by the duke of Normandy (afterwards William I. of England). Alain Fergent, one of his successors, defeated William in 1085, and forced him to make peace. But in the following century the Plantagenets succeeded in establishing themselves in Brittany. Conan IV., defeated by the revolted Breton nobles, appealed to Henry II. of England, who, in reward for his help, forced Conan to give his daughter in marriage to his son Geoffrey. Thus Henry II. became master of Brittany, and Geoffrey was recognized as duke of Brittany. But this new dynasty was not destined to last long. Geoffrey's posthumous son, Arthur, was assassinated by John of England in 1203, and Arthur's sister Alix, who succeeded to his rights, was married in 1212 to Pierre de Dreux, who became duke.
This was the beginning of a ducal dynasty of French origin, which lasted till the end of the 15th century.
From that moment the ducal power gained strength in Brittany and succeeded in curbing the feudal nobles. Under French influence civilization made notable progress. For more than a century peace reigned undisturbed in Brittany. But in 1341 the death of John III., without direct heir, provoked a war of succession between the houses of Blois and Montfort, which lasted till 1364. This war of succession was, in reality, an incident of the Hundred Years' War, the partisans of Blois and Montfort supporting respectively the kings of France and England. In 1364 John of Montfort (d. 1399) was recognized as duke of Brittany under the style of John IV., but his reign was constantly troubled, notably by his struggle with Olivier de Clisson (1336-1407). John V. (d. 1442), on the other hand, distinguished himself by his able and pacific policy. During his reign and the reigns of his successors, Francis I., Peter II. and Arthur III., the ducal authority developed in a remarkable manner. The dukes formed a standing army, and succeeded in levying hearth taxes (fouages) throughout Brittany. Francis II. (1435-1488) fought against Louis XI., notably during the War of the Public Weal, and afterwards engaged in the struggle against Charles VIII., known as "The Mad War" (La Guerre Folle). After the death of Francis II. the king of France invaded Brittany, and forced Francis's daughter, Anne of Brittany, to marry him in 1491. Thus the reunion of Brittany and France was prepared.
After the death of Charles VIII. Anne married Louis XII. Francis I., who married Claude, the daughter of Louis XII. and Anne, settled the definitive annexation of the duchy by the contract of 1532, by which the maintenance of the privileges and liberties of Brittany was guaranteed. Until the Revolution Brittany retained its own estates. The royal power, however, was exerted to reduce the privileges of the province as much as possible. It often met with vigorous resistance, notably in the 18th century. The struggle was particularly keen between 1760 and 1769, when E. A. de V. du Plessis Richelieu, duc d'Aiguillon, had to fight simultaneously the estates and the parliament, and had a formidable adversary in L. R. de C. de la Chalotais. But under the monarchy the only civil war in Brittany in which blood was shed was the revolt of the duc de Mercoeur (d. 1602) against the crown at the time of the troubles of the League, a revolt which lasted from 1589 to 1598. Mention, however, must also be made of a serious popular revolt which broke out in 1675 - "the revolt of the stamped paper."
See Bertrand d'Argentré, Histoire de Bretagne (Paris, 1586); Dom Lobineau, Histoire de Bretagne (Paris, 1702); Dom Morice, Histoire de Bretagne (1742-1756); T. A. Trollope, A Summer in Brittany (1840); A. du Chatellier, L'Agriculture et les classes agricoles de la Bretagne (1862); F. M. Luzel, Légendes chrétiennes de la Basse-Bretagne (Paris, 1881), and Veillées bretonnes (Paris, 1879); A. Dupuy, La Réunion de la Bretagne à la France (Paris, 1880), and études sur l'administration municipale en Bretagne au XVIIIe siècle (1891); J. Loth, L'émigration bretonne en Armorique du Ve au VIIe siècle (Rennes, 1883); H. du Cleuziou, Bretagne artistique et pittoresque (Paris, 1886); Arthur de la Borderie, Histoire de Bretagne (Rennes, 1896 seq.); J. Lemoine, La Révolte du papier timbré ou des bonnets rouges en Bretagne en 1675 (1898); M. Marion, La Bretagne et le duc d'Aiguillon (Paris, 1898); B. Pocquet, Le Duc d'Aiguillon et la Chalotais (Paris, 1900-1902); Anatole le Braz, Vieilles Histoires du pays breton (1897), and La Légende de la mort (Paris, 1902); Ernest Lavisse, Histoire de France, vol. i. (Paris, 1903); Henri Sée, étude sur les classes rurales en Bretagne au moyen âge (1896), and Les Classes rurales en Bretagne du XVIe siècle à la Revolution (1906).
 Certain authorities count the father of this duke, another John of Montfort (d. 1345), among the dukes of Brittany, and according to this enumeration the younger John becomes John V., not John IV., and his successor John VI. and not John V.