Duchy of Brittany, 1 January 1200

Brittany on 1 January 1200 is a duchy without its duke.

Arthur, twelve, has lived at Philip Augustus's court in Paris since the end of September 1199, a ward and a bargaining counter. His mother Constance, freed in 1198 from two years' captivity at the hands of her second husband Ranulf of Chester, governs with her third, Guy of Thouars, whom she married in the autumn of 1199; Guy counts his reign from then. The barons are largely Arthur's men, the bishops of Nantes and Vannes with them, and no Angevin garrison is known in the duchy.

The danger is not in Brittany but at the conference table: within months the two kings will settle that Arthur holds Brittany of John.

Who rules

Name: Arthur I, with Constance (duchess in her own right) and Guy of Thouars (duke by marriage)
Title: Duke of Brittany, with his mother the duchess and her husband
Since: Constance heiress since Conan IV's death (1171) and ruling since Geoffrey's death (1186); Arthur proclaimed duke and co-ruler in 1196; Guy married to Constance between August and October 1199
Born: Arthur 29 March 1187 at Nantes (aged 12); Constance about 1161 (about 38)
Family: Constance is the daughter of Conan IV and Margaret of Huntingdon. Arthur is the posthumous son of Geoffrey, Henry II's third son: nephew of King John, grandson of Eleanor of Aquitaine. Guy of Thouars is the third son of Viscount Geoffrey IV of Thouars and younger brother of Viscount Aimery VII.
Confidence: high

Wikipedia lives of Arthur, Constance and Guy, citing Everard and Jones's edition of Constance's charters.

Overlord

Disputed. Arthur did homage to Philip II in 1199 (at Le Mans, late April or May) for Brittany, Anjou, Maine and Touraine. The Angevins hold that Brittany is held of the duke of Normandy; John has received no homage for it.

The realm that morning

Governed by Constance and Guy in Arthur's name; at peace; no foreign garrison known.

Threats

A peace between Philip and John at Arthur's expense
Arthur's person in Philip's hands
Eleanor and the honour of Richmond in John's hands
Constance's health (she dies 5 September 1201)
Angevin pressure through the march barons who also hold of John (Pouancé, Fougères's Norman lands)

Ruler

Arthur I (aged 12), absent in Paris; Constance (about 38) governing with Guy of Thouars.

Consort

Guy of Thouars, Constance's husband since autumn 1199 (first joint act at Angers, October 1199); styled duke by marriage.

Heirs and children

Arthur is unmarried. His heir presumptive is his sister Eleanor, the Fair Maid of Brittany (born about 1184, about 15), held in Angevin custody; Constance later obtains her release to join Arthur in France (date not pinned). A younger sister Matilda died in childhood. Constance's daughter by Guy, Alix, is born in 1200 (day not pinned; Constance may already be pregnant). Two more daughters (Catherine, and possibly Margaret) follow in 1201.

Officers

The ducal seneschal and other household officers in post on 1 January 1200 are not pinned in the sources consulted. Peter of Dinan, bishop of Rennes from 1199, is often named as Arthur's chancellor (not verified here).

Court winter 1199 in 1200

Arthur at Philip's court in Paris. Constance and Guy were at Angers in October 1199; where they kept Christmas is not pinned (Nantes, Rennes or the Thouars country are all possible).

Treaties and wars

Arthur's homage to Philip (1199) and Philip's recognition of his claim to Anjou, Maine and Touraine; the failed Anglo-French talks of mid-August 1199, from which Arthur was excluded; the reconciliation with John at Le Mans on 22 September 1199, broken the same night when Arthur, Constance and Aimery of Thouars fled for fear of Arthur's arrest. No war on Breton soil that winter.

Marriages

Constance and Guy of Thouars (autumn 1199). Ranulf of Chester, whose marriage to Constance was dissolved (1198 or 1199), marries Clemence of Fougères, of the Breton march barony (late 1199 or 1200; sources differ).

Rome and the interdict

On 1 June 1199 Innocent III ruled that Dol is subject to Tours, ending the Breton claim to an archbishop of their own; Constance resisted and is said to have been excommunicated (date not given). The interdict decreed at Dijon falls on Philip's lands, not on Brittany.

Coinage

Ducal pennies struck at Rennes and Nantes; the Penthièvre counts strike at Guingamp (not pinned for 1200).

The host

The barons' contingents (Penthièvre, Léon, Rohan, Porhoët, Fougères, Vitré, Châteaubriant, La Guerche, Ancenis, Retz, Clisson, Dinan) and Breton foot, famous as mercenaries. No figures.

What the year holds

What happened next, if nothing in play changes it. Each event carries what it depends on and what would stop it.

In 1200

mid-January 1200Philip and John agree a truce and the outline of a peace; Arthur's Angevin claims are given up.Depends on: Philip preferring a settlement. Stopped by: Philip choosing to fight on for Arthur.
22 May 1200Treaty of Le Goulet: Philip recognises John's overlordship of Brittany; Arthur (and Constance) must do homage to John for the duchy. Arthur stays at the French court.Depends on: The truce holding. Stopped by: A breakdown before May.
1200 (day not pinned)Birth of Alix of Thouars.Depends on: Natural course. Stopped by: Mischance.

Later, on the likely course

5 September 1201Constance dies at Nantes; Arthur rules in his own right, from Paris.Depends on: Natural course. Stopped by: Not likely to be changed except by a cure.
1202Philip knights Arthur at Gournay, betroths him to his daughter Marie and launches him on Poitou; Arthur is captured at Mirebeau on 31 July 1202.Depends on: War renewed in 1202. Stopped by: The peace of 1200 holding.

Where the sources disagree

campaign notes (Part 6 B) date the Dol ruling to 1199 without a day; the Constance article gives 1 June 1199 and says Constance was excommunicated for resisting it. Worth checking before an event post.
The French life of Arthur names 'André III de Vitré' among his backers; the lord of Vitré in 1199-1203 was Andrew II.

Evidence: The family and the 1199 chronology are well attested; the duchy's officers and Constance's whereabouts that winter are not pinned.

On the map: The duchy is drawn through its lord records (Duke of Brittany for the four ducal counties and the ducal share of Léon, and the barony records) and the anchors.

Primary sources for this realm

Chronicles, registers, sagas and inscriptions written in or near 1200 that cover this entry. Each has its own page with editions, translations and where to read it.

Chronicles of the Churches of Anjou (Saint-Aubin, Saint-Serge, Saint-Florent and others), Various (monks of Angers and the Loire) (11th to 13th centuries; the Saint-Aubin annals run to the 1220s). The Angevin houses' own annals of the succession crisis in their city: Arthur received at Angers in 1199 with Constance and the Breton and Angevin barons, John's counter-moves, the defection of William des Roches and the Angevin lords to John, and the peace of 1200 that left Arthur John's vassal. Read online
The Great Chronicle of Tours, Anonymous (a canon of Saint-Martin of Tours) (about 1227). The Loire valley's view of the Angevin succession. Read online
History of the Dukes of Normandy and the Kings of England, Anonymous of Bethune (a clerk in the household of Robert VII of Bethune) (about 1220). A Flemish lord's clerk writing twenty years on, with a soldier's interest in who fought whom. Read online
The Acts of Philip Augustus, with Delisle's Calendar, Various (the French royal chancery) (1179 to 1223). The king's own charters and treaties for the year: the peace of Peronne with Baldwin IX in January 1200, the treaty of Le Goulet with John on 22 May 1200, the marriage settlement for Louis and Blanche, the privilege for the scholars of Paris, grants to towns, abbeys and Norman lords, and the first acts of the king's new acquisitions in the Vexin, Evreux and Berry. Read online

Sources and studies

Last revised 4 November 2026. Published 4 November 2026. Suggest a correction on the OMNIA Discord.