[10] The cliff-like ridge overlooks the Great War Island (Serbian: Veliko ratno ostrvo) and the confluence of the Sava river into the Danube, and makes one of the most beautiful natural lookouts in Belgrade.

Early Singidunum reached its height with the arrival of Legio IV Flavia Felix which was transferred to the city in 86 AD and remained there until the mid 5th century.

The Hungarian king Béla I gave the fortress to Serbia in the 11th century as a wedding gift (his son married the Serbian princess Jelena), but it remained effectively part of Hungary, except for the period 1282–1319.

The outbreak began in Ottoman Empire in 1836, which had no medical protocols of any kind at the time, and prince Miloš blocked the borders immediately imposing the mandatory quarantine.

[21][22] After the Ottoman withdrawal, newspapers in Austro-Hungary continuously published stories, backed by the military experts, that the fortress became strategically obsolete and that, having no value of any kind, Austrian army could destroy it in 24 hours.

[19] After the takeover of the fortress, Serbian forces kept finding parts of the gallows, chains, gibbets and impalement stakes in the dungeons, used previously by the Ottomans to torture the prisoners.

Mihailo's successor, prince and later king Milan Obrenović, ordered the leveling of the terrain in the eastern sections of the fortress and planting of the greenery and trees, which in time developed into the Kalemegdan Park.

[19] After the Third Hatt-i sharif of 1833, issued by the Ottoman sultan Mahmud II, number of Turks remaining to live in Belgrade was limited to 6,000, including women and children, and a strong Turkish garrison.

[28] The fortress and the park were damaged during World War I. Serbian army had no proper weaponry to fight the Austro-Hungarian gunboats, so they freely fired at the city from the Sava.

[29] Heavy fighting occurred in the Lower Town in 1915, when Serbian forces, led by major Dragutin Gavrilović, persistently but ultimately unsuccessfully, fought the invading Austro-Hungarian army.

Instead of everything, the railway was conducted around the foothills of the fortress, encircling it completely, and effectively cutting it off from the Sava river, which wasn't universally accepted among the architects and urbanists of the day.

[44][45] Šapić then retreated a bit, stating this is just a "political idea" which is not hastily made, that only now analyses and surveys will be done to check the viability, that nothing will be built instead of the zoo but the fortress will be conserved instead, and that there is no set time frame for the project.

Pressured financially and politically, von Reiswitz felt he must side with one of them, so he arranged the participation of Ahnenerbe with organization's head Walther Wüst in October 1941.

Based on this, collaborationist Minister for Education and Religion Velibor Jonić issued the "permit on monopoly" to Ahnenerbe's Secretary General Wolfram Sievers in February 1942.

Joined by Sievers and Herbert Jankuhn, Heinrich Himmler's close associate, Unverzagt began targeted digging, searching for the material proof to confirm the German idea of transforming Belgrade into Prinzeugenstadt.

He specifically searched for the monumental gate at the entry into the Lower Town, built during the Nicolas Doxat's rebuilding of Belgrade under the orders of Prince Eugene of Savoy in the 1720s and 1730s.

It was to be connected military with the copper and gold Bor mines and the Danube's Iron Gates gorge, to create the Banat area protection zone.

Some surviving documents show that they discovered remains of Celtic and Gothic settlements, a trench from the Roman period and relics from the Austrian rule after the conquest of Eugene of Savoy.

Detailed plan on Kalemegdan from 1965 provided that, despite the immense archaeological value that lies beneath the fortress ground, basically only what was discovered by that time can be explored, restored or protected.

Based on the findings so far, it is estimated that during the rule of despot Stefan Lazarević in the first half of the 15th century, when Belgrade became capital of Serbia, the city within the fortress had 5,600 to 12,000 inhabitants.

[52] During the tenure of mayor Dragan Đilas (2008–13), the idea of expanding the zoo to Donji Grad, which it occupied prior to the World War II, resurfaced, but the experts were against it.

[54] When the Hungarians handed over the city to Serbian despot Stefan Lazarević, he began massive reconstruction of the fortress, including the church, which was restored and expanded.

[54] Gornji Grad (Горњи Град), the upper section of fortress, turned into a park, with beautiful promenades and the statue of "The Victor" (Serbian: Pobednik), the so-called "Roman well" (Serbian: Rimski bunar), actually built by the Austrians, the Popular Observatory (since 1963) in the Despot Stefan Tower, the türbe (tomb) of Damad Ali Pasha, Mehmed Paša Sokolović's Fountain, tennis and basketball courts, etc.

[56] The magazine is today embellished with the artifacts from the Roman period which were discovered in or around the fortress: tombstone stelae, monuments, altars and the Sarcophagus of Jonah, which originates from the 3rd century AD.

It apparently was a dungeon as it was mentioned during the 1456 Siege of Belgrade when 30 Hungarian conspirators died in it after their scheme to let the Turks into the fortress and surrender the city to them was thwarted.

Within the scopes of a massive construction and reconstruction of Belgrade in the Baroque manner, from 1717 to 1731 a present facility was dug and a complex wooden mechanism was installed to lift the water up from the pit of 50 m (160 ft).

[58] Because of that, during the World War II an urban myth spread through Belgrade claiming that the gold from the National bank of the Kingdom of Yugoslavia was hidden in the well.

[69] Already existing criticism of the project continued, from the officially used name (gondola instead of a traditional Serbian žičara) and chosen location, to the route, especially the Kalemegdan station which is a collapsible locality above the cave, in the area already prone to mass wasting.

With an enlarged price of €15 million and unified opposition to the project by the environmentalists, architects and urbanists, with additional cutting of over 100 trees in Ušće park across the river, this prompted popular protests.

As a combination of several habitats (parkland with old trees, fortress, landscape view of rivers and forested Veliko Ratno Ostrvo), Kalemegdan may be interesting for overseas tourists-birdwatchers as it provides a snapshot of local bird fauna.