The 12th- and 13th-century growth in ducal resources coincided with Brittany’s
belated economic expansion as land was cleared for exploitation, notably by the
Cistercians and Hospitalers, and new urban markets founded. Breton participation in
trade (salt from the Guérande peninsula, wine from Burgundy, Caen stone) encouraged
the growth of ports in French-speaking eastern Brittany. By the 14th and 15th centuries,
towns along the northern and western coast were also engaged in the carrying trade south
to Gascony and Portugal, north to Flanders, and across the Channel to southern England,
especially Cornwall, where Breton and Cornish were mutually intelligible languages.
Increasing quantities of Breton canvas and leather products were exported.
Trade significantly altered the linguistic balance between French and Breton, as
French spread outward from major towns. In eastern Brittany, the linguistic frontier had
greatly receded by the end of the Middle Ages. The Breton aristocracy had adopted
French language and culture from the 11th century; with French and Latin as the
languages of administration, Breton was a low-status tongue. It was used by the church
for preaching; Breton literature survives from the 15th century onward and is mostly
devotional.
When Jean II (r. 1286–1305) was created a peer of France in 1297 and his right to the
ducal title finally recognized by the royal chancery, Brittany was opened to an even
greater degree of French cultural influence and royal control. Military service was
expected of the Breton duke, Breton cases were heard in the royal Parlement, royal
ordinances were extended to Brittany, and, although the ducal right to strike coin was
recognized by the crown, it was carefully monitored lest royal coinage be affected.
Growing French control nevertheless provoked a reaction, and in the 14th century royal
intervention was restricted. Ducal administrators developed notions of the duke’s
inalienable regalian rights and validated them by reference to the independent Breton
kingdom believed to have existed in the early Middle Ages.
The balance of royal and ducal interests was shattered when Jean III died in 1341,
leaving a disputed succession. For the rest of the Middle Ages, the problems of an
uncertain succession were worked out against the backdrop of the Hundred Years’ War.
In the Arrêt de Conflans (1341), Philip VI ruled in favour of Jeanne de Penthièvre and
her husband, Philip’s nephew Charles de Blois, in preference to the late duke’s half-
brother, Jean de Montfort. After Montfort’s death in 1345, Edward III intervened as
guardian of his son, the future Jean IV. The Breton civil war (1341–64) was a convenient
theater for Anglo-French hostilities. The defeat and death of Charles de Blois (Auray,
1364) led Charles V to recognize the Montfort claim and left the duchy exhausted by
ravaging, coastal pillaging, the collapse of central authority, and arbitrary exactions by
both sides. Jean IV (r. 1364–99) had the delicate task of balancing the economic
advantages of friendly relations with England with the need to keep on cordial terms with
France. He and his son Jean V (r. 1399–1442) had to reassert ducal authority in the face
of the Breton aristocracy, among whom the Penthièvre claim still had supporters and
several of whom found employment in French service (Bertrand du Guesclin, Olivier de
Clisson, and Arthur de Richemont among others). However, they were able to take
advantage of the weakness of the French crown to create an effectively independent,
well-administered duchy in which the duke’s regalian prerogatives were stressed by
fostering a sense of Breton national identity, adopting royal ceremonial, and refusing
liege homage. Frequent meetings of the Breton Estates (an advisory, legislative, and until
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