The Niš Fortress is an urban fortification in the center of the city of Niš, on the right bank of the Nišava River, which has existed for about two millennia since the first century AD, as evidenced by numerous archaeological finds. The complex of this cultural monument consists of rich cultural layers, simultaneously intertwined and connected, but also conflicting in the same relationships.

In its current state, it is one of the best-preserved fortresses in Serbia. Its polygonal base with eight bastions is built on the remains of ancient, Byzantine, and medieval fortifications. The height of the ramparts is 8 meters, with an average thickness of 3 meters, and the total length of the ramparts is 2100 meters. Outside, the fortress was surrounded by a moat, and the area inside the fortress ramparts is more than 20 hectares.

The Turkish fortress was built on the remains of ancient and medieval fortifications. In ancient times, the Niš fortification was mentioned as a strong castrum (a common type of permanent Roman military camp in antiquity), about which the sixth-century Roman historian Ammianus Marcellinus wrote that it was "repeatedly besieged but never surrendered or was defeated." The Roman stone fort was probably built around the middle of the 2nd century when the first cohort of Dardanians was stationed in Niš. It was at this time that Niš was first mentioned in written sources. In the geography of Claudius Ptolemy, Niš was listed among the four largest cities of Dardania. At the end of the second and beginning of the third century, Niš received the status of a municipality—a self-governing city. Niš might not have been widely known, but in 272 AD a significant event occurred: Emperor Constantine the Great was born here. In 313, he signed the famous Edict of Milan, which ended the persecution of Christians. Many legends surround how this happened. Some claim that before the decisive battle, the emperor dreamed of a cross. A divine voice said, "In this sign, you will conquer," and ordered the sign to be inscribed on the soldiers' shields. Other legends say that a cross hovered in the sky above the army. After these miraculous visions, Constantine won the victory, granted Christians rights and freedoms, and before his death, he himself was baptized. However, malicious tongues deny the miracles. According to one Byzantine historian, Constantine ordered the execution of his young wife and son and then, repenting, began to ask forgiveness from the Roman gods. The gods, represented by priests, refused to forgive the emperor, so he decided to change his faith.

Emperor Constantine the Great (306-337 AD) was born here, who, according to an anonymous writer, "magnificently adorned this city," built his palace in the center, and fortified the city. In 340, Constantine’s sons—Constans and Constantius—lived in Niš. In 350, the usurper Vetranion abdicated here, and in 361 Emperor Julian resided here. Finally, in 365, the brothers Valentinian I and Valens lived here. This well-fortified Roman city, according to Priscus’s records, was razed to the ground by the Huns in 441/442, but the desolation did not last long: its strategic position was too important. Niš blocked a narrow mountain pass leading from the West to the East, to Asia Minor. In 471, it also suffered from a Gothic attack.

Only during the reign of Justinian I, from 527-565, was Niš again mentioned as an administrative center, a fortified and impregnable city with restored ramparts and a military camp, around which more than thirty new fortifications were built. Procopius, in his work "On Buildings," writes that Justinian "fortified Niš and made it impregnable to the enemy." In the 6th century, Byzantine Emperor Justinian rebuilt both the city and the fortress. From ancient times, remains of buildings and an entire Byzantine street have survived. A plaque states that even mosaics and frescoes have been preserved and that excavations are not yet finished.

The restored Niš Fortress was first attacked by Slavs in 550. Their invasions of Thessaloniki and Constantinople through Niš were recorded in 578, 579, 584, 586, and 587. In the 6th century, Niš and its fortifications are mentioned several times in sources.

The Slavs finally conquered Niš around 615. Devastated and mostly abandoned by the Roman population, Niš remained in Slavic hands. This marks the beginning of the medieval period of the city. By the 10th century, the Niš fortification had acquired all the characteristics of a medieval fortress. In a charter of Byzantine Emperor Basil II to the Ohrid Archbishopric in 1020, the Niš diocese was also recorded.

In the summer of 1040, during Peter Delyan’s uprising against Byzantine rule, the Niš fortress was held by rebels for some time. From 1048 to 1050 and in 1080, Pecheneg hordes besieged the Niš fortress and plundered its surroundings. In the summer of 1072, Hungarian King Solomon conquered Niš and took the hand of St. Procopius, and in September, the rebel army captured the city and remained there until December 1072. When the Crusaders first passed through Niš in 1096, they described it as better fortified than Belgrade, surrounded by "strong walls and towers."

The first written source about the restoration of the medieval Niš fortress dates back to 1165, when Byzantine historian John Kinnamos claimed that Emperor Manuel I Komnenos (1143-1180) "surrounded Niš with walls." Serbian sources report that in 1183, the great prefect Stefan Nemanja entered the "glorious city of Niš" and destroyed it to the ground, and in 1186, he reconquered it from Byzantium and rebuilt it, receiving the German Emperor Frederick I Barbarossa in Niš in 1189. Byzantium reconquered it again in 1190. Serbian King Stefan the First-Crowned is mentioned in Niš from 1214 to 1215. After that, throughout the 13th century, there are no mentions of the city in sources, probably because it was under Bulgarian rule.

After the Battle of Velbazhd in 1330, when Stefan Dečanski defeated Bulgarian Emperor Michael Shishman, Niš again became part of Serbia. During the reign of Prince Lazar (1371-1389), the Niš fortress was rebuilt, and in 1386 Niš was conquered by the Turks for the first time, and the fortress was destroyed. During the Serbian Despotate, from 1402 to 1427, Despot Stefan Lazarević conquered Niš and restored the fortress. This was the last restoration of the medieval Niš fortress, as Niš finally fell under Turkish rule in 1428. At the very beginning of Turkish rule, the Niš fortress was destroyed twice. In November 1443, a combined Serbian-Hungarian army led by Đurađ Branković and János Hunyadi liberated Niš and advanced to Sofia, and on the return journey in January 1444, passed through Niš again. In 1454, despots Đurađ and Hunyadi again destroyed Niš.

Then came the Turks, who at first did not restore the medieval fortress. At the end of the 17th century, Austrian troops invaded deep into Turkish territories and captured Niš in 1690. They built two bastions in the fortress, which, however, did not help them, as a year later the Ottomans retook the fortress but soon lost Belgrade. After recapturing the city, they only reinforced the ramparts in several places. But after losing Belgrade in 1717 during the Austro-Turkish War and moving the military and administrative center to Niš, in 1718 the Turks built the earthen fortification Hisar in just one year. It was larger than the present fortress and had the shape of a triangle, including the Belgrade Mahala. The earthen rampart of Hisar had seven bastions, and along the ramparts ran a moat 3.5 meters wide, filled with water from the Nišava. The appearance of Hisar is preserved on the so-called Italian plan of 1719. The fortress ramparts were built from February 1719 to June 1723.

The present artillery-type fortification was built by the Ottomans between 1719 and 1723 on the site of the ancient and medieval fortifications.

By a Sultan’s decree dated February 19, 1719, it was decided to build a powerful fortress in Niš. In the spring of the same year, work began according to the project of chief architect Mehmed-aga and his brother Mustafa-aga, the chief organizer of the works. In the first year of construction, 1719, he hired more than ten thousand spahis from ten sanjaks of the Rumelia beylerbeyliks, and in 1722 from 14 sanjaks. In the last year of rampart construction in 1723, 40 masters were brought from Constantinople; in total, 400 stonemasons built the ramparts. The completion of the works was marked by celebrations and the installation of a memorial plaque with an inscription on the Istanbul Gate in June 1723.

Like any artillery fortification, today’s Niš Fortress has a polygonal base with seven unequal sides and four large gates (Stambol Gate, Belgrade Gate, Vodena or Jagodina Gate, and Vidin Gate), one small gate (the so-called exit to the city ramparts), and eight bastions.

The eastern part of the fortress was considered prestigious. Military personnel and nobility lived there, and the most beautiful house was occupied by Mithad Pasha. The building was called "Pasha’s Konak," the ruler’s residence. Wherever the Ottomans came, they built the so-called "Islamic trio": a mosque, a caravanserai, and a hammam. The Niš fortress was no exception. The hammam, built in the 15th century, became a marvel of engineering, with a system of scoops, reservoirs, and pipes that purified, heated, and supplied water to the room. This building can still be admired today. It is located right at the entrance to the fortress. The inner part of the city had many cafes, grocery shops, boza sellers, blacksmith workshops, numerous wheelwright workshops, and other craft workshops, as well as various other Turkish "shops."

In 1878, the fortress housed three large Turkish mosques out of thirteen built in Niš: the Hamaz-bey or Niš Mosque, located in the Balia Edren district near the Belgrade Gate, on the left side of the main city street (coinciding with today’s main fortress path at the beginning of the ascent); the mosque of Bali-beg Djedrenjan (reconstructed in 1976/77) without a minaret still stands in the fortress. Next to this mosque, Mithad Pasha also built a library that operated until 1877.

The third mosque, about which nothing is known today, was located at the highest part of the fortress. Inside the fortress, there were also architecturally interesting clock and fire towers, as well as many other buildings later demolished.

In the 1930s, near the fortress ramparts, a monument to the Muslim saint Zaida-Badža was erected in the form of a miniature mosque, which was also visited by Orthodox Christians. It was built by Niš Roma on their donations.

On November 21, 1940, a monument to those shot in 1915-1918 was consecrated and opened during excavations.

After liberation, the fortress served a purely military role until 1950, when the army left the fortress, and since then it has been preserved only as a historical monument.

Sources:

https://sr.wikipedia.org/wiki/Нишка_тврђава

https://balkanist.ru/gorod-nish-i-ego-tverdynya/городом.