In the Middle Ages, the Counts of Provence built a fortress in the 11th century marking the border between Provence and Languedoc, inherited from the Partition of Verdun (843) carried out on the death of the Carolingian king Louis Le Pieux. Through the interplay of the dynastic successions of the counts of Burgundy-Provence, Tarascon also falls within the territories of the Holy Roman Empire from 1032.

In 1233, the inhabitants took the side of the counts of Toulouse and opposed their lord, the count of Provence. They claim their local privileges, and destroy the fortified site. The castle was partly rebuilt at the end of the 13th century. A mint was installed there in 1272.

During the Hundred Years War (1337-1453), the fortress was at the heart of the battles of Provence. Bertrand du Guesclin, in the pay of Louis I of Anjou, leader of the French party, laid siege to Tarascon in 1368. The Angevin prince was designated as heir to the county of Provence in 1380 by Queen Jeanne. From then on, the Dukes of Anjou became the new masters of Tarascon and endeavored to have their authority, which was disputed, recognized.

From 1400 to 1411, Louis II (1377-1417), prince builder, rebuilt a monumental fortress whose work was entrusted to Jean Robert, master of the works of the king. His son, Louis III (1403-1434), completed the building on the city side from 1429 to 1435. From its height of 46 meters, the castle thus asserts the power and authority of the Dukes of Anjou over the entire territory of the country of 'Arles.

The castle of good King René

René I inherited the county of Provence on the death of his brother Louis III in 1434. Born in 1409 in Angers, he was the second son of Louis II and Yolande of Aragon. He died in exile in Aix-en-Provence in 1480.

Throughout his reign, René I stayed in Provence: in Tarascon, Arles, Marseille, Aix-en-Provence and Avignon. The Château de Tarascon then became a place of power and prestige.

In the fortress built by his father and his brother, he carried out utilitarian, comfort and decoration improvements. He built a private oratory for his wife Isabelle de Lorraine, opened several doors and windows, and built a chapel for the singers.

René Ier commissioned decorations characteristic of the life of a prince of the Middle Ages, such as the painted panels depicting characters and familiar and fantastic animals, called closoirs. These still adorn the larch wood ceilings of the Castle.