Château de Dinan

The first stronghold at Dinan, known as the vieil chastel or Châteauganne, was a motte-and-bailey built from the 11th century on a promontory north-east of the town, outside today's ramparts. In 1064 William, Duke of Normandy, campaigned against Brittany, with Harold Godwinson — later his rival at Hastings — taking part; the Bayeux Tapestry depicts the campaign's capture of Dol-de-Bretagne, then Rennes, where Conan II, Duke of Brittany, had taken refuge after fleeing Dol, and then Dinan, where Conan surrendered the keys of the city at the point of a lance. The tapestry also shows the besieged attempting a sortie across a bridge over the motte's ditch while two attackers try to set fire to the palisade guarding its central tower.

The Châteauganne motte was destroyed around 1170; only its name survives, attached to the sub-prefect's residence that now stands on the site.

Victorious in the War of the Breton Succession, which had kept the town's defences under upgrade until 1365, John IV, Duke of Brittany, ordered a keep built at Dinan in 1380 to assert his authority over a town that had long supported his rival Charles de Blois. Under the master builder Étienne le Tur, the work was completed by 1393, and the tower may already have been in use by 1384. Known today as the Donjon de la duchesse Anne, it stands near the Saint Louis gate as part of the 2,600 metres of medieval ramparts, begun in 1283, that still encircle the old town, with a moat and drawbridge separating it from both the country outside and the town within — a stronghold against outsiders and townspeople alike.

At the end of the 16th century Dinan became a stronghold of the Catholic League, and under the Duke of Mercœur, governor of Brittany, the castle was substantially reworked between 1595 and 1598. An underground passage, the souterrain Mercœur, was built to connect the keep to the Tour Coëtquen, an artillery tower raised at the end of the 15th century, and in the process the Porte du Guichet — the town's former south gate — was walled up. A raised courtyard protected by spur-shaped defences was added at the same time. The new gun embrasures faced the town rather than the countryside beyond it.

Left derelict during the 17th century, the castle was surveyed twice, in 1693 and 1701, by the military engineer Siméon Garangeau, who praised its architectural quality and proposed converting the keep first into a residence for the town's governor and then into a military prison. Through the 18th century, English sailors taken prisoner were housed there by the hundreds. The conversion cost the building its original roof, permanently replaced by a terrace, and a new entrance was cut through the chevet of its chapel.

Listed as a monument historique in 1886, the castle had by then served as a common-law prison through the 19th century. The town of Dinan bought it in the early 20th century and opened a municipal museum there in 1908, its collections devoted to the history and crafts of Dinan and the villages along the Rance.

Those collections were progressively removed from the castle from 2015 and are now kept in municipal storage. A restoration and reinterpretation programme launched by the town in 2014 opened the souterrain Mercœur to visitors for the first time on 9 June 2019, alongside new displays on fifteenth-century warfare and daily life in the ducal residences. By 2019, with more than 55,000 visitors that year, the castle was the most-visited monument in the town and the second most-visited château in the Côtes-d'Armor, after Fort la Latte.