The Château de Vincennes on the eastern edge of Paris, France, boasts the tallest medieval castle keep (donjon) in Europe, standing at approximately 52 meters (170 feet). Built in the 14th century during the reigns of Philip VI and Charles V, this massive limestone tower served as a fortified royal residence and a symbol of the Valois dynasty's power. Its walls are over three meters thick, designed to withstand the siege technology of the Middle Ages. The keep is part of a larger fortress complex that functioned as a secondary seat of the French monarchy before the rise of Versailles. While other structures like the "Tower of London" or "Castel del Monte" are famous, none match the sheer verticality of the Vincennes donjon. In 2026, visitors can climb the spiral staircases to the upper floors, which once housed the king's private apartments and a library. The tower's architectural significance is bolstered by its survival through centuries of conflict, including its use as a state prison and its occupation during the Napoleonic wars and World War II.