Osijek's Tvrdja complex was built in the 18th century with impressive defensive walls and town gates, Romanic nucleus and rectangular main square, so the Osijek is the most important military, economic, administrative and cultural center of Slavonia.
Tvrdja belongs to most important old Croatian town nucleuses and it has the greatest harmony of Baroque military buildings preserved until today.
Standing out is the main guard building from 1730, with arcades and a square tower for guard patrols. Elongated one-story barracks are known under names like Neutor, Donati, Zeichenamt, Jugend Kaserne.
Preserved in Tvrdja are beautiful aristocratic and citizen buildings, Baroque circular pillar of the Holy Trinity (1729-1730), fountain, Museum of Slavonia building, old gymnasium, church of St. Michael with valuable inventory and accessories (kept here is the chalice with enamel medallions with images from the life of St. Francis Xavier, with a stamp from Vienna from 1764).
Franciscan monastery was founded in 1699, and it was the place of the first faculty in Slavonia in 1735 (philosophy and theology studies). In the same year the first printing house in Slavonia was established here.
Osijek's Upper Town is a historical treasure trove: old sacral, cultural and historical monuments, Capuchin monastery, Neo-Gothic church of Sts. Peter and Paul, St. Anna chapel, classicist palace of the Virovitica County, theatre building, chambers of commerce…
Located in the Lower Town is a series of late Baroque citizen houses, series of Secessionist and late Baroque buildings in the New Town, and in Retfala the valuable Pejacevic family castle (18th century), and the church of Ascension of the Holy Cross with the Mausoleum of Count Pejacevics.
Temporal administration (1735 - 1737) with a beautiful portal and two Baroque pools made of reddish Baranja stone in front of the building from year 1761 is one of the most magnificent buildings in Slavonia.
One of the oldest buildings in Osijek is the municipality and town seat building (1700 - 1702). Valuable portraits of Slavonian large estate owners from the 18th century can be found in the Gallery of Fine Arts.