Belgrade Fortress: Danube, Sava and the Strategic Geography of Serbia’s Capital

Stand on the ramparts of the Belgrade Fortress and the reason it exists lies spread out below you. Two rivers meet at the foot of the ridge: the Sava, coming in from the west, and the much broader Danube, sweeping on towards the east. Whoever held this headland watched both, and for more than two thousand years Celts, Romans, Byzantines, Hungarians, Serbian despots, Ottoman sultans and Habsburg emperors fought to be that power. On our small group Balkans history tour, the fortress is part of the morning city tour on Day 5 in Belgrade.

Why the Belgrade Fortress matters on a Balkans route

It is tempting to treat the Belgrade Fortress as a pleasant park with old walls, the green space where the capital goes to walk on a weekend. Its real interest lies in what it guarded. Britannica describes Belgrade as lying at the confluence of the Danube and Sava rivers, at the convergence of three historically important routes of travel between Europe and the Balkans. A fortress on that point controlled river traffic, the crossings between the Pannonian plain to the north and the Balkan interior to the south, and the roads that led towards Constantinople and the Aegean.

That makes the fortress an unusually clear place to read the region’s past. The official guide to the complex, published by the public company that manages it, puts the layering in one sentence: Roman walls underlie Serbian ramparts, on top of which the Ottomans and Austrians built their fortifications. Here, many empires are stacked on one hill. Our overview of the whole Balkans history route follows those empires from Dubrovnik to Kotor; in Belgrade they meet on a single ridge, and the walls show each one’s turn at holding the confluence.

Two rivers and a ridge: the geography of the confluence

The fortress stands on the end of a ridge that drops steeply to the water. The historian Jona Lendering, writing for the ancient history site Livius, describes the Sava as rising in what is now Slovenia and the Danube as emptying into the Black Sea, and notes that anyone travelling from northern Italy or the Adriatic towards the east would have had to pass this high, flat-topped hill. North of the rivers lies open, level country; south of them the land rises into the hills of Serbia. The confluence is where those two worlds touch.

Rivers in this part of Europe were both highways and borders. For long periods the Danube marked the edge of an empire, so a fortress here faced a frontier as well as a crossing. Supplies, armies and trade moved along the water, and a garrison on the ridge could see an approach long before it arrived. Our article on how mountains, plains and climate have shaped Balkan societies traces that pattern across the peninsula. At Belgrade it is concentrated into one headland, and it explains why the site was fought over so often: the official fortress guide records that it has been razed to the ground and rebuilt many times.

The geography also explains the fortress’s shape. The Upper Town occupies the high ground, where the main defensive works face inland; the Lower Town stretches down to the riverbank, where a port and its defences once stood. The two halves, high and low, inland and riverside, are the basic division of the complex, and they reflect the two jobs the fortress always had: to resist an army coming overland and to control the water.

Singidunum: a Roman base on the Danube frontier

People lived on this ridge long before Rome. The fortress administration traces settlement back to the Neolithic, and Livius records that the site was occupied by the Celtic tribe of the Scordisci in the Late La Tène period. The fortress guide places the Celtic Singidunum in the district of Karaburma rather than on the Upper Town, so the walls on the ridge belong to later builders.

Livius records that the Romans reached the area during Octavian’s Dalmatian War of 35–34 BCE, and over the following century the Danube became a heavily garrisoned frontier. According to Livius, after the Dacians crossed the river and defeated the frontier legions in 86 CE, the emperor Domitian divided the province of Moesia in two, and the Fourth Legion Flavia Felix was given the defence of Upper Moesia from the table mountain now known as Kalemegdan. The Tourist Organisation of Serbia says that in the 2nd century CE the site became the legion’s permanent military camp. Other legionary bases stood at Viminacium, downstream along the Danube, and at Sirmium, up the Sava, so Singidunum was one link in a chain of fortresses guarding the river line.

The tour page describes the Belgrade visit as taking in “the large fortress parts of which date back to the early Roman period”, and the Tourist Organisation of Serbia notes that the ramparts of the Upper Town are built on the foundations of the Roman castrum. A civil town grew up alongside the camp; Livius places its forum and baths near today’s Students’ Square and notes that some of Belgrade’s streets still follow the ancient grid. Singidunum was also the birthplace of Jovian, emperor briefly in 363 and 364. In the late Roman period the city was overrun in turn by Huns, Sarmatians, Gepids and Ostrogoths, and in 584, Livius records, it fell to the Avars.

Between Byzantium, Hungary and Serbia

The Byzantine emperor Justinian rebuilt the walls in the sixth century; the fortress guide dates his work to around 535, and Livius cites Procopius’s account of it in the Buildings. Over the following centuries the hill changed hands many times. Slavic settlers arrived in the region, and the city acquired the Slavic name it still carries: Beograd, which Britannica glosses as “White Fortress”. Byzantium rebuilt the defences again in the twelfth century, and according to the fortress guide Hungary held the city for much of the thirteenth and fourteenth centuries, with Serbian rule interrupting at times.

The Serbian period that left a lasting mark came in the fifteenth century. After the Battle of Kosovo in 1389 the medieval Serbian state was much reduced, and its ruler, Despot Stefan Lazarević, made Belgrade his capital; the City of Belgrade dates his rule there from 1403, and the fortress guide gives 1404 for the city becoming the capital. He rebuilt the walls, raised a castle in the Upper Town and divided the city into the Upper and Lower Towns that still define the site. The Tourist Organisation of Serbia says the fortress saw its golden age in the fifteenth century, during his reign. Our longer account of Serbia’s history from the Nemanjić rulers to the modern state sets this period in the wider story of medieval Serbia.

The Lower Town’s river defences grew with the threat. The fortress administration dates the Nebojša Tower, on the Danube side, to around 1460, by which time the city was again under Hungarian rule; it was built to defend the entrance to the Lower Town port. Its later history is darker: the same source records that it became a dungeon, and that the Greek patriot Rigas Feraios was imprisoned and killed there in 1798. The tower was renovated in cooperation with the Greek government, work the fortress administration says was completed in 2010.

1456 and 1521: the fortress on the Ottoman frontier

After Despot Stefan’s rule ended in 1427, the City of Belgrade records, his successor Đurađ Branković was forced to surrender the town to the Hungarians, and it became the hinge of Hungary’s southern defences against the advancing Ottoman Empire. In 1456 the sultan Mehmed II, the conqueror of Constantinople, laid siege to the city. Britannica’s biography of the Hungarian commander János Hunyadi describes how he provisioned and armed the fortress, collected an army and won a victory on 22 July 1456 in which the siege was raised. Hunyadi died of an epidemic in the camp on 11 August, less than three weeks later. Britannica’s judgement is that Hungary was saved from Ottoman conquest for 70 years.

That reprieve ended at Belgrade too. In 1521 Sultan Süleyman I, known in the West as Suleiman the Magnificent, took the city, and Britannica records that five years later his army defeated Hungary at Mohács on the Danube, and that in 1529 he laid siege to Vienna. Belgrade had been the obstacle in the way; once it fell, the river route north lay open. For the next century and a half the fortress was an Ottoman base on the road to Central Europe, part of the empire that our article on the Ottoman Empire, its art and its golden age under Suleiman describes at its height.

Ottoman Belgrade inside the walls

The Ottoman centuries left their own names and buildings on the hill. The fortress administration notes that the Ottomans called the open field in front of the walls Kalemegdan, and the Tourist Organisation of Serbia explains the name as a combination of two Turkish words, kale, fortress, and megdan, battlefield. The name stuck, and it is used for the park and often loosely for the whole fortress.

Among the Ottoman works that survive, the fortress administration lists the fountain of Sokollu Mehmed Pasha and the tomb of Damat Ali Pasha. The first name links Belgrade to the day before: Sokollu Mehmed Pasha, known in Serbian as Mehmed Paša Sokolović, is the grand vizier on whose orders, UNESCO records, the bridge at Višegrad was built at the end of the sixteenth century. The group stops to view that bridge on Day 4, before crossing into Serbia. The Tourist Organisation of Serbia also notes that the towers of the Zindan Gate in the Upper Town were used as prisons during Ottoman rule, a reminder that a fortress was a place of confinement as well as defence.

How much walking does the Belgrade Fortress visit involve?

The tour page does not give a walking distance for the Day 5 city tour, but the tour as a whole is rated Level 2, Moderate. Participants must be able to carry their own luggage, climb and descend stairs, and take part in 3 to 5 hours of physical activity a day, the equivalent of walking up to 8 kilometres on uneven ground. The fortress sits on a ridge, with the Upper Town on the high ground and the Lower Town down by the river, so paths and steps link different levels. If you would like to talk through the walking on this day, a Tour Specialist can go over it with you.

Habsburg bastions and the treaties of 1718 and 1739

The Ottoman defeat outside Vienna in 1683 turned the tide, and Belgrade became the prize of a long contest between the Ottoman and Habsburg empires. The fortress guide records that Austria took the city in 1688 and began a modern fortress there, and that the Ottomans retook it in 1690, when an explosion destroyed Despot Stefan’s castle. During the Austro-Turkish war of 1716–18, Prince Eugene of Savoy took Belgrade in August 1717, and by the Treaty of Passarowitz of 21 July 1718, Britannica records, Austria received Belgrade with parts of northern Serbia.

The two decades that followed shaped much of what a visitor sees. During the Austrian period (1717–1739), the fortress was rebuilt in the 1720s and 1730s to designs by the Swiss engineer Nicolas Doxat de Démoret, turning the medieval stronghold into an artillery fortress of angled bastions, ditches and gates. The Tourist Organisation of Serbia singles out the lavishly decorated Gate of Charles VI in the Lower Town, named after the Habsburg emperor, as a Baroque gate of that period. It did not last long as a Habsburg possession. The Treaty of Belgrade of 1739 returned the city to the Ottomans and, the fortress guide records, required the demolition of the new fortifications.

The contest continued through the century. The fortress administration dates the Clock Tower, a 27.5-metre tower with Baroque elements, to the middle of the eighteenth century, and Britannica records that the Austrian field marshal Gideon Ernst von Laudon captured Belgrade from the Ottomans once more in 1789. Each change of ruler brought rebuilding, demolition or both, which is why the walls mix medieval stonework with Baroque brick in a way that can be hard to untangle without a guide.

From uprising to park: 1806 to 1928

The next change came from within Serbia. During the First Serbian Uprising, insurgents took the town of Belgrade at the end of 1806, and the Ottoman garrison in the fortress gave way early in 1807. Ottoman rule later returned, and an Ottoman garrison stayed in the fortress for decades. The fortress administration records the end of that chapter: in 1867 the keys were handed to Prince Mihailo Obrenović, and the fortress passed into Serbian hands.

With the garrison gone, the old killing ground in front of the walls could become a garden. The fortress guide dates the start of landscaping in Kalemegdan Park to 1869 and says the park took its present form between the two World Wars; it is divided into Great and Little Kalemegdan Park. A monument that the City of Belgrade says is often used as a symbol of the city came in 1928. The City records that Ivan Meštrović’s bronze Victor, about 14 metres tall with its column, was raised on Kalemegdan for the tenth anniversary of the breach of the Thessaloniki Front, after a fountain Meštrović had designed in 1912 was abandoned. The Military Museum also stands in the park, and the fortress and park have been under state protection since 1946, the fortress guide notes.

How does the fortress fit into Day 5?

The fortress is part of the morning city tour of Belgrade on Day 5. The tour page adds a visit to the Royal Palace, but only if the day is a Saturday or Sunday. The day also includes the Residence of Princess Ljubica, built in the nineteenth century and now a museum showing how the nobility lived at the time, and the afternoon is free to take in the market and the old parts of the city, which leaves room to return to Kalemegdan Park if you wish.

Which other fortresses does the tour visit in Serbia?

Two more follow within a few days. On Day 6 the group visits Manasija, which the tour page calls a fifteenth-century fortress monastery, and on Day 8 a guided tour of Niš takes in its fortress. Our article on Niš, the Roman Naissus, and its fortress covers that stop, the next major city on the road south.

The Belgrade Fortress in the sequence of the route

Seen in order, the fortress answers one question again and again: who controls the meeting of the Sava and the Danube? Each power that held the ridge left a layer, and only in the nineteenth century, when the last garrison left, did the battlefield in front of the walls become a park.

That makes the Belgrade Fortress a useful key to the rest of Serbia. Travelling in a small group of up to 16 travellers with an Odyssey Program Leader, mature travellers arrive in Belgrade after the Ottoman bridge at Višegrad and then head south to Topola, Manasija and Niš, where the same empires appear again in different proportions. Standing above the two rivers on Day 5, with the plain stretching away to the north and the hills rising to the south, it is easy to see why this one headland mattered so much to so many powers.