Château de Châteaudun was built between the 12th and 16th centuries. The Count of Blois Thibaut V had the keep built around 1170. The Sainte-Chapelle was built between 1451 and 1493. The choir and the high chapel were built between 1451 and 1454, with the nave and the oratory between 1460 and 1464. Jehan de Dunois, the bâtard d'Orléans (Bastard of Orléans), built the west wing (the "aile Dunois") between 1459 and 1468. The bell tower was erected in 1493.
François I of Orléans-Longueville began construction of the north wing between 1469 and 1491. The upper floors were added by François II d'Orléans-Longueville and his descendants during the first quarter of the 16th century.
Today the castle includes a keep, a chapel (Sainte-Chapelle), the Dunois wing and the Longueville wing. Château de Châteaudun overlooks the Loir river. Perched on a limestone outcrop, it shows its origins as a 12th century fortress. Converted during the Renaissance into a comfortable residence, the main body of the building is roofed in the gothic style. It still has, notably, a finely carved staircase from this period. Renovated since the 1930s, the castle has been classed as a historic monument since 1918.
References:Bomarsund fortress and garrison was built in 1832-1854 by Russian Empire to defence Åland Islands against enemies. British and French fleet attacked against it during the Crimean War in 1854. After a week of fighting the British stormed the remaining fort. Anglo-French forces destroyed it totally after battle. In the Treaty of Paris 1856, the entire Åland Islands were demilitarized, which is a status that has been preserved until this day.
Nowadays there are some ruins left and fortress area is open for visitors.