To thank him for his role in the Battle of Bouvines in 1214, King Philippe Auguste offered the site of Montleroy to Chancellor Guérin, bishop of Senlis. Half of the land was sold to build the Abbey of Victory and on the rest was built a residence for the Bishops called Mont-l’Évêque.
The Bishop set up his summer residence in the old fortified house on the banks of the Nonette River. Over the centuries, the castle is improved by additions and especially by the arrangement of the river to create ponds and supply water to mills. It was destroyed during the Hundred Years’ War and then rebuilt during the 16th century. It remained the property of the bishops of Senlis until the french Revolution.
The buildings are organized on the edge of a pond in the middle of a vast and remarkable park. In the center, the 18th century house built to receive the administrative services of the diocese, on each side the castle and the chapel.
The buildings were purchased in 1806 by Baron Joseph-Xavier de Pontalba. The family had the facades of the castle and the chapel facing it completely redesigned in the neo-gothic or “troubadour” style. It is a question of reviving the medieval arts by decorating the facades with crenellations, arrows and gargoyles. Mont-l’Évêque is even considered to be one of the rare successful examples of this romantic style. A special feature in the chapel is the rood screen of the Carmelite convent in Metz, dating from the 14th century. It was for a long time stored in wooden crates in the home of Josephine de Beauharnais and bought by the Pontalba family, close to Napoleon’s wife.
The outside visit of the castle is authorized by the owner, a direct descendant of Joseph de Pontalba.
First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.