Smederevo Fortress Smederevo Fortress ( ) , in Smederevo , Serbia , was a medieval fortified city and temporary capital of Serbia in the Middle Ages . It was built between 1427 and 1430 , on the order of Despot Đurađ Branković , the ruler of the Serbian Despotate . It was further fortified by the Ottoman Empire , that had taken the city , in the end of the century . Smederevo is the largest medieval lowland type of fortresses in Europe . The fortress withstood several siege s between the Ottomans and Serbs , which it survived relatively unscathed . It was not until World War II that it was heavily damaged , by explosions and bombing . As of 2009 it is in the midst of extensive restoration and conservation work , despite which the fortress remains " one of the rare preserved courts of medieval Serbian rulers . " Smederevo Fortress was declared a Monument of Culture of Exceptional Importance in 1979 , and is protected by the Republic of Serbia . In 2010 , the fortress was placed on the Tentative List for possible nomination as a World Heritage Site ( UNESCO ) . Location . Smederevo Fortress , 45 kilometers southeast of Belgrade , covers 11 . 3 hectares in the center of the modern - day city of Smederevo . It is strategically located on the right bank of the Danube river on the triangular plain formed by the confluence of the Danube and Jezava rivers , only 72 meters above sea level . This location allowed the Serbian capital to remain near the Christian Kingdom of Hungary , while also satisfying Sultan Murad II of the Ottoman Empire by eliminating the uncontrolled passage of the Hungarians into the Morava valley . The fortress ' position connecting the Balkans and Central Europe has made it an important religious and commercial center for centuries , now aided by being on the Pan - European X corridor . The Danube also connects it to many other historic sites , most notably Belgrade and its suburb of Vinča , Novi Sad , Golubac fortress , Lepenski Vir and Viminacium . History . Amidst the turbulence of the Ottoman conquest of the Balkans in the early 15th century , the region ' s Christian rulers lost several battles , such as the Battle of Kosovo and the siege of Veliko Tarnovo . Despot Stefan Lazarević had to maintain the Serbian Despotate in a delicate balance between the Ottomans and Hungarians . Around 1403 , he accepted the Hungarian vassalage from King Sigismund and established the new capital in Belgrade , which was ceded to him as an award . After Stefan ' s death in 1426 , Đurađ Branković , Stefan ' s nephew and successor , had to return Belgrade to the Hungarians . To compensate for this loss , Đurađ decided to build a new capital , and the choice fell to Smederevo . Smederevo , which had no prior settlement , was chosen for several reasons . In 1428 , during the , the Hungarians and Ottomans agreed to recognize Branković as an independent ruler of Serbia , thereby turning it into a buffer state . A contract also established Ottoman overlordship of Serbia , in conjunction with remaining a Hungarian vassal . Between the longer status with Hungary and religious differences with the Ottomans ( Hungary and Serbia were Christian , as compared to the Muslim Turks ) , it was preferred that the capital be closer to Hungary than the Ottoman Empire . Smederevo ' s location on the Danube , between Belgrade and Golubac , provided easy access to other points along the river . It also allowed the control of Danube traffic , including blocking Hungarian entry into the Morava valley , which satisfied the Turks . In the fall of 1428 , construction of the capital began . In 1430 , the first part of the fortress , including a palace and enough other buildings to form an inner city , was completed . Work on a fortified suburb and additional fortifications continued until 1439 . On April 20 , 1434 , Đurađ Branković ' s youngest daughter Katarina and Ulrich II of Celje were wed in the new fortress . This marriage stressed the friendly relations the Despot had with the Ottoman Porte , however , as Ulrich ' s kinship with the Hungarian Queen implied an increased Serbo - Hungarian alliance . As a result , Vizier Mehmet Saridže - pasha arrived in Smederevo in mid - 1434 with a message from Edirne . It stated that Serbia ' s safety from the Ottoman Empire could only be guaranteed through the marriage of Branković ' s older daughter to Sultan Murad II . After much deliberation , the council convoked at the palace conceded , and arrangements were made for Mara to be engaged to the Sultan . That autumn , Murad sent several of his " most famous viziers " to retrieve his fiancée . On August 14 , 1435 , a formal contract of " brotherhood and friendship " between Serbia and the Republic of Venice was signed in Smederevo ' s audience hall . This contract resulted in Đurađ and his sons being counted as Venetian citizens . In early June 1439 , the peace with the Ottomans , which had been gained through Mara ' s marriage to the Sultan , was broken . Led by Murad II , 130 , 000 Turkish soldiers occupied the hills around Smederevo . Branković rushed to Hungary for help , leaving his son Grgur in command . Help was not forthcoming , but Smederevo withstood the attack , even when Murad brought in cannon s . Nearly three months later , on August 18 , 1439 , hunger forced the Serbs to surrender . Princes Grgur and Stefan were sent to Anatolia and blinded , despite the pleas of their sister , now Sultana Mara . Five years later , however , Smederevo , Grgur , and Stefan returned to Branković through the Peace of Szeged . Around the beginning of 1449 , Branković imprisoned Hungarian regent John Hunyadi in the dungeons of the fortress , but he was ransomed by his countrymen . In 1453 , Sultan Mehmed II and Isak - bey Arbanazović led another attack on Smederevo as part of a devastating raid on Serbia . The Turks took 50 , 000 men , women and children during that raid , but Smederevo was well - led by Thomas Kantakouzenos . Despite having only 6 , 000 men , compared to the Ottomans ' 20 , 000 , the city withstood . Smederevo was besieged by Mehmed the Conqueror for the second time and by Ottomans in general for the third time in 1456 , ending up again defeated by the Serbians . In 1459 , Smederevo was captured by the Ottomans , leading to the end of the medieval Serbia n state . During World War II , German forces used the fortress for ammunition storage . On June 5 , 1941 , the ammunition exploded , blasting through the entirety of Smederevo and reaching settlements as far as 10 kilometers away . Much of the southern wall of the fortress was destroyed , the nearby railway station , packed with people , was blown away , and most of the buildings in the city were turned into debris . Around 2 , 500 people died in the explosion , and every other inhabitant was injured or wounded ( approximately 5 , 500 ) . Bombing by the Allies in 1944 caused further damage . Current and future use . The fortress is currently used as a city park , and occasionally hosts festivals , concerts , fair s , and other cultural events . A stage has been built in the inner city . To the southeast , the previously open space along the Jezava now has a harbor and a marina . There are also discussions underway to determine compatible future , modernized uses , and to develop projects to restore and rehabilitate the fortress . Cultural and historical significance . Smederevo Fortress has been described as " one of the most striking and monumental pieces of architecture surviving from medieval Serbia " , and " the witness of Serbian creative force . " It is an accurate display of traditional medieval defensive architecture and has remained well preserved , suffering no major deterioration until World War II . The fortress and surrounding area have accumulated evidence of the civilizations that developed throughout history , mainly between the 15th and 20th centuries , providing a direct testimony for the progress of the medieval Serbian state and corresponding Orthodox Church . The fortress was built by Đurađ Branković as the new capital of Serbia . During construction , Branković ' s wife Jerina was seen speaking with the foreign overseers — her brother George Kantakouzenos and his men — which resulted in her being commonly associated with the project . Among the workers , this association , coupled with required long - term labor and high taxes , gained her the nickname " Prokleta Jerina " ( Damned Jerina ) . The amount of effort exerted also produced a variety of exaggerations and stories , such as the epic poem " " Starina Novak i knez Bogosav " " ( " Elder Novak and Count Bogosav " ) , which stated that many people fled to the woods and became hajduci in order to escape taxes and further work . While there were in fact hajduci in the area , it is unclear whether they were actually related to the fortress ' construction . Once the first part was completed , Smederevo Fortress quickly became an important connection between the Balkans and central Europe . Shortly after it was built , the city reached its peak importance as a religious , commercial , and trade center , at which point it was populated mainly by Serbs and colonies of merchants , primarily from Dubrovnik . Around the same time , the relics of Saint Luke the Evangelist , who became the patron saint of Smederevo , were brought and stored in the church in the fortress . In relation to the structure itself , the inner city is notable for the audience hall , which is an important representation of Serbian medieval architecture . High in the stone wall on the Danube side , four sets of double - arched windows are carved in a combination of Gothic and Romanesque styles . This is where a merchant contract between the Republic of Venice and the Serbian Despotate was signed . There is also a tower in the inner city with a large brick inscription naming Đurađ Branković and stating the date of construction . It reads „ " V Hrista Boga blagoverni despot Gurg , gospodin Srblju i Pomorju zetskomu ; zapovešću njegovom sazida se ovaj grad v leto 6938 " “ ( " In Christ the Lord faithful despot Gurg , Lord of Serbs and the Littoral of Zeta . By His order this city was built in the year of 6938 [ 1430 ] " ) . Above it is an immured cross , which gives the tower its names " " krstata kula " " and " " krstača " " . This type of inscription is rare , and found only on former Byzantine territory . It is the sole example in Yugoslavia . In the fortified suburb are the minimal remains of two more significant structures . One was a sacral complex , " Blagoveštenjska crkva " ( Annunciation Church ) , where the Saint ' s relics were stored . Though its construction began in the 15th century , it was built over several historical phases . The second structure was a Turkish bath from the 17th century . For years , Smederevo Fortress stood as the last defense against Ottoman assaults . During their attack in 1439 , it also became the first site in Serbia to see cannon fire . When it fell in 1459 , it became the center of a Turkish sanjak . Later , Smederevo was a province of the Habsburg Monarchy , and between 1805 – 1807 it was once again the center of the renewed Serbian state . Architecture . Smederevo Fortress is a monumental complex built in the Byzantine tradition and modeled after Constantinople fortress . Although its foundations were not intended to be submerged , it is classed as a water fortress because it is completely surrounded by water . After the fortress ' completion , there was a decline in its military importance and few structural changes were made . As a result , the original architectural style has been preserved to this day . The fortress is encircled by 1 . 5 kilometers of crenelated walls over 2 meters thick , and 25 towers which are each approximately 25 meters tall . Two sides were bordered by the Danube and Jezava rivers , though the Jezava has now been redirected away from the wall . The third side had two moats added to the defensive system , one for the inner city and one for the suburb . The area south of the outer walls was left open . Construction . There were four main phases in the construction of the fortress . The work on the first part , a fortified manor for Despot Đurađ Branković built at the confluence of the rivers , began in the autumn of 1428 . Under the eye of George Kantakouzenos , older brother of Despotina Jerina Branković , lumber , lime , and enormous stones from the former Roman cities of Mons Aureus ( the modern village of Seone , west of Smederevo ) , Margum ( at the mouth of the Great Morava ) , and Viminacium were collected . In the spring of 1429 , Greek and Ragusan workers began the brickwork . In 1430 , the elegant manor was completed . It included a palace stretching along the length of the moat wall ; a throne hall against the Danube wall ; a keep , " Donžon kula " ( Donjon tower ) , in the corner formed by the walls ; a treasury in a high chamber ; and other auxiliary buildings , creating an inner city . The throne hall , where Branković received his visitors , was built with four double - arched windows , fashioned in a mixed Gothic / Romanesque style . " Donžon kula " was intended to be the final line of defense . It was constructed with walls over 4 meters thick , and housed the nobility during Turkish attacks . Hidden doors were built into the Jezava wall , allowing for passage towards Hungary . The next nine years were spent expanding the fortifications to include a larger fortified suburb , thereby finishing the main fortress . In the suburb , a sacral complex was built in phases from the 15th century onwards , and a Turkish bath was added by the Ottomans in the 17th century . There was a ship gate in the suburb ' s Danube wall , where sailors could enter the fortress . It is unclear whether any long - term residential buildings were built . Between 1460 – 1480 , while held by the Ottoman Empire , a larger defensive system was built , including escarpments , low walls , and more towers . During the first half of the 18th century , fortified trenches were added . Current condition . The state of deterioration of the fortress ranges widely , from " krstata kula " which is still well preserved , to sections of the walls which have seen no repair work and have collapsed in some places . The first , and most severe , damage happened during World War II . On June 5 , 1941 , ammunition stored in the fortress exploded , destroying not only a large part of the southern wall , but also decimating most of Smederevo . Further damage was caused by the Allies ' bombing in 1944 . A dam in the Iron Gate , completed in 1972 , raised the water level of the lower Danube basin and caused significant flooding . Between 1970 – 1980 , a system was built to protect the fortress and surrounding city from future high water , however there was once again major flooding in 2006 , a result of heavy rainfall and melting snow . The fortress has been the focus of restoration and conservation efforts , followed by archaeological and architectural research , since at least 1970 . The majority of work so far was done between 1970 – 1995 . While some parts were at least partially repaired , others only received conservation work and are still in bad condition . In the inner city , the foundation is the only part of the palace which remains standing , and the audience hall has only an outline where the base was . What remains has been partially restored and is now stable , though issues of vegetation growth and permanent maintenance remain . The surrounding towers also still need work , as many have collapsed . The town ' s restoration was followed in 1994 – 1995 with an archaeological investigation . The fortified suburb is still in very bad condition . Parts of the wall are missing and several towers are leaning or partially collapsed . The corner tower behind the Turkish inscription tower , and the stretch of wall along the Danube have seen conservation efforts , and the southern wall , which has been restored several times as part of a levee , is stable , but the conservation work is of poor quality . Much of the time has instead been spent on archaeological excavations and research , especially of the remains of the sacral complex and Turkish bath . The escarpment along the Danube , which had partially collapsed several times , has seen restoration work , and is now in good condition . On the other sides , much of the escarpment is gone or underground , and the overall condition is unknown . The ambiance and setting are also threatened , though they remain the best along the Danube . The other two sides are surrounded by modern development , such as a marina on the eastern side , a railway to the south , and a variety of other urban structures . The planned final result of the work is for full rehabilitation of both Smederevo Fortress and its immediate surroundings , including relocating the railroad , though estimations of cost vary widely . Between 2003 – 2004 , the cost for just the conservation work was estimated to be €10 , 600 , 000 , while the total rehabilitation cost , including conservation , restoration , and research , reached as high as €22 , 000 , 000 . In 2005 , the combined cost for basic conservation and research dropped to €4 , 000 , 000 . Ongoing risk factors . Despite conservation efforts , the fortress is still at risk of damage , for reasons , both natural and man - made . The higher groundwater level resulting from the dam in the Iron Gate threatens its stability , and has increased the number of floods , especially before the coast was consolidated . Air pollution and vegetation growth are increasing the rate of decay . Urban encroachment , especially by the railroad , continues to threaten the character of the area surrounding the fortress . Unrestricted visits by tourists , combined with inadequate protection , maintenance , and support , both administrative and financial , also contribute to the slow deterioration of the fortress .