Tvrđa Tvrđa ( " Citadel " ) is the Old Town of the city of Osijek in Croatia . It is the best - preserved and largest ensemble of Baroque buildings in Croatia and consists of a Habsburg star fort built on the right bank of the River Drava . Tvrđa has been described by the World Monuments Fund as " a unique example of an eighteenth - century baroque military , administrative , and commercial urban center " . The star fort was constructed in the immediate vicinity of medieval Osijek after the defeat of the Ottoman forces in 1687 , due to Osijek ' s strategic importance . The official construction began on August 1 , 1712 and was supervised by the city and fort ' s commander , General Johann Stephen von Beckers . Constructed to plans by Mathias von Kaiserfeld and then Maximilian Gosseau de Henef it was inspired with the Lowlands ( Dutch ) fortress ' of its time . All five planned bastion s and two gate s were complete by 1715 . By 1735 , the inner town was finished and three northern bastions had been added . When complete , it was the largest and modern Habsburg fortress on the border of the Ottoman Empire . It consisted of eight bastions , two armouries , two major depots , the garrison headquarters building , the military court , the construction office , the garrison physician , the guardhouse , officer apartments , the military hospital and seven barracks . The fort was entirely surrounded with walls and palisades and had four main gates at each side ( north , south , east , west ) . Tvrđa had street lights by 1717 and was the site of the first public water supply in Croatia , opened in 1751 with sewage system built shortly after in 1760 , while horsecar was added in 1884 . Tvrđa ' s military importance decreased after the Berlin Congress of 1878 , with the increasing stability of the surrounding region . Most of the fort walls and fortifications were destroyed in the 1920s due to the obstacle they presented to the development of Osijek . While the fortifications have largely been removed , the fort ' s interior core remains intact and is now home to churches , museums , schools and other public buildings , as well as numerous bars and restaurants . Of the fortification system only the northern side of the walls remain as well as parts of the 1st and the 8th bastion along with the northern gates known as ' Water Gates ' ( ' Vodena vrata ' ) . Tvrđa sustained significant damage during the Croatian War of Independence during the 1990s and was featured on the 1996 World Monuments Watch List of Most Endangered Sites . It now features on on Croatia ' s ' tentative list ' for consideration for nomination as a World Heritage Site . History . Medieval and Ottoman eras . The new name of Osijek first appeared in 1196 . The centre of medieval Osijek was on the banks of the River Drava where Tvrđa now stands . The town was a trade and port settlement from the early 12th century due to its position on the way from Pécs and Buda southwards . The site was home to the Romanesque church of the Holy Trinity . Between 1526 and 1687 , Osijek was ruled by the Ottomans , who did not change the layout of the settlement in any substantial way but introduced Islamic places of worship , giving the area an Oriental appearance . Traces of the medieval and Ottoman towns remain to this day , including a remnant of the old Ottoman fortress wall , known today as the " Turkish Wall " ( ) or " Filibey ' s Fort " ( ) , lying next to the Tvrđa access road . During the Ottoman period , Osijek was internationally known because of the Suleiman Bridge . The construction of the bridge was begun by İbrahim Pasha on August 16 , 1526 following the orders of Suleiman the Magnificent . The bridge , which connected Osijek and Darda , took the form of a wooden road on piers and was approximately long and wide . Seen as a great threat to Christian Europe , the bridge was attacked several times , being destroyed in 1664 , when it was set on fire on the orders of the Croatian feudal lord Nicholas VII of Zrin ( , ) . The bridge was rebuilt during the rule of Suleiman II . Finally , it was burned down by the Austrian army in 1686 . Design and construction . First layout in late 17th century . Development of a military settlement at Tvrđa started in 1687 when the Habsburg armies drove the Ottomans out of the city during the Great Turkish War . The chief commander of the Imperial army , Louis William , Margrave of Baden - Baden , saw Osijek as a location of exceptional strategic importance in the war against the Ottomans . He urged the repair of the city walls , and proposed construction of a new fort according to Vauban ' s principles of military engineer ing . The town magistrate was established in 1690 , while the plans of the new fort were still being drawn up , and one of its documents from August of the same year described the condition of the settlement as " ruinous " . Two months later , on October 29 , the Ottoman army suddenly attacked . The attack was repulsed only owing to a well - organised defence , and the Turks withdrew on November 6 , after a brief siege . The event was a clear lesson that construction of the fort must not be delayed any further . The first phase of Tvrđa ' s conversion into a Baroque fortress was based on the plan devised by the engineer Mathias von Kaiserfeld from 1691 . Second layout in 18th century . The original plan for Tvrđa was drafted because of the need to reinforce the town walls , but did not include provisions to redesign the interior and envisaged largely uncontrolled development . New plans for a fort on the right bank of the River Drava were drawn up by Maximilian Gosseau de Henef . Gosseau took over planning of the fort when construction was already under way . Starting in 1712 , Austrian engineers built barracks , staff headquarters , churches and monasteries , surrounded by system of moat s , bastions and gun positions , respecting Gosseau ' s design . By 1715 , all five planned bastions and two gate s were complete . The construction of the outwork on the opposite bank of the River Drava , designed to offer protection from the north and to serve as a bridgehead , was completed by 1721 . Construction of the inner town was completed by 1733 , and in 1735 an additional three northern bastions were completed , along with a post office , the fort ' s construction office and the hospital . The completed fort had " eight bastions , two armouries , two major depots , the garrison headquarters building , the military court , the construction office , the garrison physician , the guardhouse , officer apartments , the military hospital and seven barracks " . Based on the ' ring model ' , the fortifications took up an area of , making Tvrđa the largest fortress on the border of the Ottoman Empire . Gosseau ' s plan left space for churches to be built where mosques had once stood . Initially , converted mosques were used as churches , but the Franciscans started to build a Baroque church in 1709 and it was consecrated in 1732 . A Franciscan monastery was built between 1699 and 1705 , with a new wing being added between 1731 and 1733 , which subsequently became a new monastery in 1761 . In 1725 , the Jesuits commenced construction of the parish church of St . Michael ( ) , following the construction of their own monastery . This church was in use after 1734 , despite being incomplete . A Holy Trinity column was erected in the fort ' s main square in 1730 as a plague monument featuring volute s with pedestals on which four protectors against the plague are placed . Four additional pedestals were added to the monument in 1784 , each featuring a statue of a saint . Tvrđa had street lighting as early as 1717 . The first system to supply public water in Croatia was opened in Tvrđa in 1751 . In the mid - 18th century there were reportedly more than 35 inn s in Tvrđa , estimated to account for one in three of the fort ' s buildings . Crown prince Joseph stayed in one of the inns when visiting Osijek . In 1786 , as Joseph II , he decreed the merger the Upper Town , the Lower Town and Tvrđa into one single town council . 19th and 20th century . As early as the second half of the 18th century , there was little or no new construction taking place in Tvrđa , and even maintenance of the fort became a burden . In 1809 Osijek was granted free royal town status . Osijek ' s council was accommodated in a building at the south - eastern corner of Tvrđa ' s main square . Tvrđa ' s military importance decreased after the Berlin Congress of 1878 as a result of increasing political and military stability in the region . Two north - western bastions were demolished in the 1870s , making way for Ambrose ' s Park ( ) . Construction of the Royal Grammar School was started in 1881 , and the Royal General Secondary School was completed in 1890 . An episcopal seminary was built in the south - western corner of the main square in 1898 . These were the only buildings erected within the Tvrđa walls in the last three decades of the 19th century . As Osijek grew as a city , the fort ' s presence hindered the potential for urban development . The demolition of most of the fort walls happened between 1923 and 1926 , with the construction of an electric tramway . The last gunpowder magazine , located behind the church of St . Michael , was demolished in 1958 . While most of the fortifications have been demolished ( only the first and eighth bastions and the northern wall and Water Gate were kept ) , the centre of Tvrđa remains intact . Yugoslav People ' s Army maintained a garrison and a military hospital in Tvrđa , but in the 1980s these buildings were gradually being abandoned , and adapted into ateliers for local painters and sculptors . The fort sustained considerable damage during the Croatian War of Independence , which lasted from 1991 until 1995 . The war brought structural damage from collapsing roofs , walls and floors . These damages threaten plaster , sculpture and murals that lack proper protection and are subject to continuing decay . Present day . After the fortress ' s military importance decreased at the end of the 19th century , Tvrđa became a center of administrative , educational , cultural , and scholarly life in Osijek and whole region . The first school in Osijek was organized at Tvrđa ; the first scholarly curriculum was introduced in 1707 , to be later expanded and renewed , and the first printing press started working in 1735 . The significance of educational institutions of Tvrđa is best underlined by the fact that Croatian Nobel Prize laureates , Lavoslav Ružička and Vladimir Prelog , were alumni of the Tvrđa schools . The Faculty of Agriculture of the Josip Juraj Strossmayer University of Osijek has occupied the former general headquarters since 1995 after its previous site was destroyed in the Croatian War of Independence . The Faculty of Food Technology has been relocated to a building that served as the first military hospital in Osijek , from the mid - 17th century until the beginning of the 1990s . Other present - day educational institutions in Tvrđa include the II and the III Gymnasium , Franjo Kuhač Music School ( former Roman Catholic Seminary ) , Jesuit Classical Gymnasium ( former logistics barracks built in the mid - 18th century ) , and the Secondary School of Economics ( former grammar school for girls ) . According to the 2001 census , within the Tvrđa city district , there are 10 , 227 inhabitants living in 3 , 310 households . The fort interior is now a centre of Osijek ' s nightlife . There are numerous bars and restaurants in Tvrđa . The fort hosts the Museum of Slavonia , the largest general - type museum in Croatia , located in Tvrđa since 1946 . The former town museum and archives building today houses the State Directorate for Monument Protection , a department of the Croatian Ministry of Culture . The patron saint of the Tvrđa is Saint Michael , and his feast day of September 29 is celebrated as the day of the Tvrđa city district . Heritage status . The World Monuments Fund has described Tvrđa as " a unique example of an eighteenth - century baroque military , administrative , and commercial urban center " . Tvrđa is on Croatia ' s ' Tentative List ' for consideration for nomination as a World Heritage Site . During the 1991 – 95 conflict in Croatia , 90 per cent of the buildings in Tvrđa were damaged to some extent and the fort was featured on the 1996 World Monuments Watch List of Most Endangered Sites . It has not appeared on the list , published every two years , since . The building of the general headquarters , dating from 1726 , and the ground plan of the fortress are depicted on the reverse of the Croatian 200 kuna banknote , issued in 1993 and 2002 . The Agency for Restoration of Osijek Tvrđa ( ) was established in 1999 . Its stated goals are protection , restoration and revitalisation of Tvrđa . The restoration process aims to preserve architectural , historical and aesthetic qualities of Tvrđa in full accordance with the restoration principles set by the International Council on Monuments and Sites , while maintaining its multifunctional character . International cooperation is also envisioned , in particular with the Council of Europe . The Agency is jointly funded by the Government of Croatia , Osijek - Baranja County and the City of Osijek .