Dating back to the 13th century, Porrentruy Castle is an imposing edifice and comprised many more buildings in its heyday. During the reign of Prince-Bishop Jacob-Christoph Blarer of Wartensee, the castle underwent an extensive period of reconstruction by the architect Nicolas Frick around 1588. In 1697, it suffered a huge fire. The courtyard is enclosed to the south by the long Princess Christina Wing, which was named in memory of visits made by Christina of Saxony, the aunt of Louis XVI and Abbess of Remiremont from 1773 to 1775. Today, the castle is the seat of the judicial authorities of the Republic and Canton of the Jura. The building’s interior is not open to the public at weekends.
The Réfous Tower, which was probably built shortly after 1271, can be found near the castle. A conical roof was added to the crenellations in the 16th century. A door leading to the tower’s second floor is positioned about 9 meters from the ground, and was once accessible by a wooden bridge leading to the Lydda building. The bridge was constructed in the 14th century and destroyed in 1804. The tower is accessible to the public via a staircase.
The Coq Tower is attached to the north-east corner of the former chancellery. It is a huge round building with four floors and features a central pillar supporting circular vaults. The window openings date back to 1756. The tower was used to store the archives of the former diocese of Basel until 1898. The armorial emblems of the Blarer of Wartensee family are painted on the side of the tower facing the town.