Hagia Sophia, officially the Hagia Sophia Grand Mosque  and formerly the Church of Hagia Sophia is a Late Antique place of worship in Istanbul. Built in 537 as the patriarchal cathedral of the imperial capital of Constantinople, it was the largest Christian church of the eastern Roman Empire (the Byzantine Empire) and the Eastern Orthodox Church, except during the Latin Empire from 1204 to 1261, when it became the city's Roman Catholic cathedral. In 1453, after the Fall of Constantinople to the Ottoman Empire, it was converted into a mosque. In 1935 the secular Turkish Republic established it as a museum. In 2020, it re-opened as a mosque.

Built by the eastern Roman emperor Justinian I as the Christian cathedral of Constantinople for the state church of the Roman Empire between 532 and 537, the church was then the world's largest interior space and among the first to employ a fully pendentive dome. It is considered the epitome of Byzantine architecture[4] and is said to have "changed the history of architecture".[5] The building was designed by the Greek geometers Isidore of Miletus and Anthemius of Tralles. The present Justinianic building was the third church of the same name to occupy the site, the prior one having been destroyed in the Nika riots. Being the episcopal see of the ecumenical patriarch of Constantinople, it remained the world's largest cathedral for nearly a thousand years, until Seville Cathedral was completed in 1520. Beginning with subsequent Byzantine architecture, Hagia Sophia became the paradigmatic Orthodox church form and its architectural style was emulated by Ottoman mosques a thousand years later, It has been described as "holding a unique position in the Christian world",[7] and architectural and cultural icon of Byzantine and Eastern Orthodox civilization.

The church was dedicated to the Holy Wisdom, the Logos, the second person of the Trinity. Its patronal feast falls on 25 December (Christmas), the commemoration of the incarnation of the Logos in Christ. Sophia is the Latin transliteration of the Greek word for wisdom and, although sometimes referred to as Sancta Sophia, 'Saint Sophia', it is not connected with Sophia the Martyr. The centre of the Eastern Orthodox Church for nearly one thousand years, the building witnessed the excommunication of Patriarch Michael I Cerularius officially delivered by Humbert of Silva Candida, the papal envoy of Pope Leo IX in 1054, an act that is commonly considered the start of the East–West Schism. In 1204, it was converted by the Fourth Crusaders to a Roman Catholic cathedral under the Latin Empire, before being restored to the Eastern Orthodox Church upon the return of the Byzantine Empire in 1261. The doge of Venice who led the Fourth Crusade and the 1204 Sack of Constantinople, Enrico Dandolo, was buried in the church.

After the Fall of Constantinople to the Ottoman Empire in 1453, it was converted to a mosque by Mehmed the Conqueror. The patriarchate moved to the Church of the Holy Apostles, which became the city's cathedral. Although some parts of the city had fallen into disrepair, the cathedral had been maintained with funds set aside for this purpose, and the Christian cathedral made a strong impression on the new Ottoman rulers who conceived its conversion The bells, altar, iconostasis, ambo and baptistery were removed and relics destroyed. The mosaics depicting Jesus, his mother Mary, Christian saints, and angels were eventually destroyed or plastered over.[17] Islamic architectural features were added, such as a minbar (pulpit), four minarets, and a mihrab – a niche indicating the direction of prayer (qibla). From its initial conversion until the construction in 1616 of the nearby Sultan Ahmed Mosque, aka the Blue Mosque, it was the principal mosque of Istanbul. The Byzantine architecture of the Hagia Sophia served as inspiration for many other religious buildings from the Hagia Sophia, Thessaloniki and Panagia Ekatontapiliani to the Blue Mosque, the Şehzade Mosque, the Süleymaniye Mosque, the Rüstem Pasha Mosque and the Kılıç Ali Pasha Complex.

The complex remained a mosque until 1931, when it was closed to the public for four years. It was re-opened in 1935 as a museum by the secular Republic of Turkey.[18] According to data released by the Ministry of Culture and Tourism, Hagia Sophia was Turkey's most visited tourist attraction in 2015 and 2019.

In early July 2020, the Council of State annulled the Cabinet's 1934 decision to establish the museum, revoking the monument's status, and a subsequent decree by Turkish president Recep Tayyip Erdoğan ordered the reclassification of Hagia Sophia as a mosque.

The Topkapı Palace  is a large museum in the east of the Fatih district of Istanbul in Turkey. In the 15th and 16th centuries it served as the main residence and administrative headquarters of the Ottoman sultans. Construction, ordered by the Sultan Mehmed the Conqueror, began in 1459, six years after the conquest of Constantinople. Topkapı was originally called the "New Palace" to distinguish it from the Old Palace ) in Beyazıt Square. It was given[by whom?] the name Topkapı, meaning Cannon Gate, in the 19th century. The complex expanded over the centuries, with major renovations after the 1509 earthquake and the 1665 fire. The palace complex consists of four main courtyards and many smaller buildings. Female members of the Sultan's family lived in the harem, and leading state officials, including the Grand Vizier, held meetings in the Imperial Council building.

After the 17th century, Topkapı gradually lost its importance. The sultans of that period preferred to spend more time in their new palaces along the Bosphorus. In 1856 Sultan Abdulmejid I decided to move the court to the newly built Dolmabahçe Palace. Topkapı retained some of its functions, including the imperial treasury, library and mint.

Dolmabahçe Palace was ordered by the Empire's 31st Sultan, Abdülmecid I, and built between the years 1843 and 1856. Previously, the Sultan and his family had lived at the Topkapı Palace, but as the medieval Topkapı was lacking in contemporary style, luxury, and comfort, as compared to the palaces of the European monarchs, Abdülmecid decided to build a new modern palace near the site of the former Beşiktaş Sahil Palace, which was demolished. Hacı Said Ağa was responsible for the construction works, while the project was realized by architects Garabet Balyan, his son Nigoğayos Balyan and Evanis Kalfa (members of the Armenian Balyan family of Ottoman court architects).The construction cost five million Ottoman gold lira, or 35 tonnes of gold, the equivalent of ca. $1.5 billion in today's values.

The Maiden's Tower, also known as Leander's Tower (Tower of Leandros) since the medieval Byzantine period, is a tower on a small islet at the southern entrance of the Bosphorus strait 200 m (220 yd) from the coast of Üsküdar in Istanbul, Turkey. There are many legends about the construction of the tower and its location. According to one legend, an emperor had a much beloved daughter and one day, an oracle prophesied that she would be killed by a venomous snake on her 18th birthday. The emperor, in an effort to thwart his daughter's early demise by placing her away from land so as to keep her away from any snakes, had the tower built in the middle of the Bosphorus to protect his daughter until her 18th birthday. The princess was placed in the tower, where she was frequently visited only by her father.

On the 18th birthday of the princess, the emperor brought her a basket of exotic sumptuous fruits as a birthday gift, delighted that he was able to prevent the prophecy. Upon reaching into the basket, however, an asp that had been hiding among the fruit bit the young princess and she died in her father's arms, just as the oracle had predicted, hence the name Maiden's Tower.

The older name Leander's Tower comes from another story about a maiden: the ancient Greek myth of Hero and Leander. Hero was a priestess of Aphrodite who lived in a tower at Sestos, at the edge of the Hellespont (Dardanelles). Leander (Leandros), a young man from Abydos on the other side of the strait, fell in love with her and would swim every night across the Hellespont to be with her. Hero would light a lamp every night at the top of her tower to guide his way.

Succumbing to Leander's soft words, and to his argument that Aphrodite, as goddess of love, would scorn the worship of a virgin, Hero allowed him to make love to her. This routine lasted through the warm summer. But one stormy winter night, the waves tossed Leander in the sea and the breezes blew out Hero's light, and Leander lost his way, and was drowned. Hero threw herself from the tower in grief and died as well. The name Maiden's Tower might also have its origins in this ancient story. Due to the vicinity and similarity between the Dardanelles and the Bosphorus, Leander's story was mistakenly attributed to the tower.

The Galata Tower, called Christea Turris (the "Tower of Christ" in Latin) by the Genoese, is a medieval stone tower in the Galata/Karaköy quarter of Istanbul, Turkey, just to the north of the Golden Horn's junction with the Bosphorus. It is a high, cone-capped cylinder that dominates the skyline and offers a panoramic vista of Istanbul's historic peninsula and its environs. The Romanesque style tower was built as Christea Turris ("Tower of Christ") in 1348 during an expansion of the Genoese colony in Constantinople. Galata Tower was the tallest building in Istanbul at 219.5 ft (66.9 m) when it was built in 1348.[3] It was built to replace the old Tower of Galata, an original Byzantine tower named Megalos Pyrgos ("Great Tower") which controlled the northern end of the massive sea chain that closed the entrance to the Golden Horn. That tower was on a different site and was largely destroyed in 1203, during the Fourth Crusade of 1202–1204.

Beyazıt Square is a square in the district of Fatih, situated in the European part of Istanbul, Turkey. It is officially named Freedom Square, but is known as Beyazıt Square after the Bayezid II Mosque on one side of it. The Square is the former site of the Forum of Theodosius built by Constantine the Great. On one side of the square is the main entrance of Istanbul University; the Beyazıt Tower is on the university's campus and can be seen from the square.

The Grand Bazaar in Istanbul is one of the largest and oldest covered markets in the world, with 61 covered streets and over 4,000 shops on a total area of 30,700 m2, attracting between 250,000 and 400,000 visitors daily. In 2014, it was listed No.1 among the world's most-visited tourist attractions with 91,250,000 annual visitors. The Grand Bazaar at Istanbul is often regarded as one of the first shopping malls of the world.

Blue Mosque, also known as the Sultan Ahmed Mosque, is an Ottoman-era mosque located in Istanbul, Turkey. A functioning mosque, it also attracts large numbers of tourist visitors. It was constructed between 1609 and 1616 during the rule of Ahmed I. Its Külliye contains Ahmed's tomb, a madrasah and a hospice. Hand-painted blue tiles adorn the mosque’s interior walls, and at night the mosque is bathed in blue as lights frame the mosque’s five main domes, six minarets and eight secondary domes It sits next to the Hagia Sophia, the principal mosque of Istanbul until the Blue Mosque's construction and another popular tourist site.

After the Peace of Zsitvatorok and the crushing loss in the 1603–18 war with Persia, Sultan Ahmet I decided to build a large mosque in Istanbul to reassert Ottoman power. It would be the first imperial mosque for more than forty years. While his predecessors had paid for their mosques with the spoils of war, Ahmet I procured funds from the Treasury, because he had not gained remarkable victories. The construction was started in 1609 and completed in 1616.

The German is a gazebo styled fountain in the northern end of old hippodrome (Sultanahmet Square), Istanbul, Turkey and across from the Mausoleum of Sultan Ahmed I. It was constructed to commemorate the second anniversary of German Emperor Wilhelm II's visit to Istanbul in 1898. It was built in Germany, then transported piece by piece and assembled in its current site in 1900. The neo-Byzantine style fountain's octagonal dome has eight marble columns, and dome's interior is covered with golden mosaics.

The Basilica Cistern, or Cisterna Basilica, is the largest of several hundred ancient cisterns that lie beneath the city of Istanbul, Turkey. The cistern, located 150 metres (490 ft) southwest of the Hagia Sophia on the historical peninsula of Sarayburnu, was built in the 6th century during the reign of Byzantine Emperor Justinian I. Today it is kept with little water, for public access inside the space.

This subterranean cistern, in Greek kinsterne , was called Basilica because it was located under a large public square on the First Hill of Constantinople, the Stoa Basilica. At this location, and prior to constructing the cistern, a great Basilica stood in its place, built between the 3rd and 4th centuries during the Early Roman Age as a commercial, legal and artistic centre. The basilica was reconstructed by Illus after a fire in 476.

Ancient texts indicated that the basilica contained gardens, surrounded by a colonnade and facing the Hagia Sophia. According to ancient historians, Emperor Constantine built a structure that was later rebuilt and enlarged by Emperor Justinian after the Nika riots of 532, which devastated the city.Historical texts claim that 7,000 slaves were involved in the construction of the cistern. The enlarged cistern provided a water filtration system for the Great Palace of Constantinople and other buildings on the First Hill, and continued to provide water to the Topkapı Palace after the Ottoman conquest in 1453 and into modern times.

The Aqueduct of Valens was a Roman aqueduct system supplying Constantinople, the capital of the Eastern Roman empire. Completed by Roman Emperor Valens in the late 4th century AD, the Aqueduct of Valens was in use for many centuries, extended and maintained by the Byzantines and the Ottomans.

The final and most visible aqueduct bridge in the system survives in the Fatih district of Istanbul, Turkey, named in Turkish: Bozdoğan Kemeri, lit. 'Aqueduct of the Grey Falcon'. The Bozdoğan Kemeri remains one of the most important landmarks of the city and Atatürk Boulevard (Atatürk Bulvarı) passes under its arches. Bozdoğan Kemeri spans the valley between the hills occupied today by the Istanbul University and the Fatih Mosque, formerly the site of the Church of the Holy Apostles. The surviving section is 921 metres long, about 50 metres less than the original length.
 
The construction of a water supply system for the city (then still called Byzantium) had begun already under the Roman emperor Hadrian. Under Constantine I, when the city was rebuilt and increased in size, the system needed to be greatly expanded to meet the needs of the rapidly growing population.
 
The Valens aqueduct, which originally got its water from the slopes of the hills between Kağıthane and the Sea of Marmara, was merely one of the terminal points of this new wide system of aqueducts and canals—which eventually reached over 250 kilometres (160 mi) in total length, the longest such system of Antiquity—that stretched throughout the hill-country of Thrace and provided the capital with water. Once in the city, the water was stored in three open reservoirs and over a hundred underground cisterns, such as the Basilica Cistern, with a combined capacity of over one million cubic metres.
 
The water comes from two lines from the north-east and one coming from the north-west, which join together outside the walls, near the Adrianople Gate (Edirne Kapı). Near the east end of the aqueduct there is a distribution plant, and another lies near Hagia Sophia. The water feeds the zone of the imperial palace. The daily discharge in the 1950s amounted to 6,120 cubic metres (216,000 cu ft). During Byzantine times, two roads important for the topography of medieval Constantinople crossed under the eastern section of the aqueduct.

The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul in Turkey) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built.

Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger, saving the city, and the Byzantine Empire with it, during sieges from the Avar-Sassanian coalition, Arabs, Rus', and Bulgars, among others. The advent of gunpowder siege cannons rendered the fortifications vulnerable, but cannon technology was not sufficiently advanced to capture the city on its own, and the walls could be repaired between reloading. Ultimately, the city fell from the sheer weight of numbers of the Ottoman forces on 29 May 1453 after a six-week siege.
 
The walls were largely maintained intact during most of the Ottoman period, until sections began to be dismantled in the 19th century, as the city outgrew its medieval boundaries. Despite the subsequent lack of maintenance, many parts of the walls survived and are still standing today. A large-scale restoration program has been under way since the 1980s.

The Süleymaniye Mosque (Magnificent Suleiman Mosque) is an Ottoman imperial mosque located on the Third Hill of Istanbul, Turkey. The mosque was commissioned by Suleiman the Magnificent and designed by the imperial architect Mimar Sinan. An inscription specifies the foundation date as 1550 and the inauguration date as 1557. Behind the qibla wall of the mosque is an enclosure containing the separate octagonal mausoleums of Suleiman the Magnificent and that of his wife Hurrem Sultan (Roxelana). For 462 years, the Süleymaniye Mosque was the largest mosque in the city, until it was surpassed by the Çamlıca Mosque in 2019. The Süleymaniye Mosque is one of the best-known sights of Istanbul, and from its location on the Third Hill, it commands a spectacular view of the city around the Golden Horn.

The interior of the mosque is almost a square, 59 metres (194 feet) in length and 58 metres (190 feet) in width, forming a single vast space. The dome is flanked by semi-domes, and to the north and south arches with tympana-filled windows, supported by enormous porphyry monoliths. Sinan decided to make a radical architectural innovation to mask the huge north-south buttresses needed to support these central piers. He incorporated the buttresses into the walls of the building, with half projecting inside and half projecting outside, and then hid the projections by building colonnaded galleries. There is a single gallery inside the structure, and a two-story gallery outside.
 
As with other imperial mosques in Istanbul, the Süleymaniye Mosque was designed as a külliye, or complex with adjacent structures to service both religious and cultural needs. The original complex consisted of the mosque itself, a hospital (darüşşifa), primary school, public baths (hamam), a caravanserai, four Qur'an schools (medrese), a specialized school for the learning of hadith, a medical college, and a public kitchen (imaret) which served food to the poor. Many of these structures are still in existence, and the former imaret is now a noted restaurant. The former hospital is now a printing factory owned by the Turkish Army.

Zeyrek Mosque or Monastery of the Pantocrator, is a significant mosque in Istanbul, made of two former Eastern Orthodox churches and a chapel. It represents the most typical example of architecture of the Byzantine middle period in Constantinople and is, after Hagia Sophia, the second largest religious edifice built by the Byzantines still standing in Istanbul. Between 1118 and 1124 Byzantine Empress Irene of Hungary built a monastery on this site dedicated to Christ Pantokrator ("Christ Almighty"). The monastery consisted of a main church also dedicated to Christ Pantocrator, a library and a hospital.
 
After the death of his wife, shortly after 1124, Emperor John II Komnenos built another church to the north of the first dedicated to the Theotokos Eleousa ("the merciful Mother of God"). This church was open to the population and served by a lay clergy. Finally, a south courtyard and an exonarthex were added to the complex, and the two shrines were connected with a chapel dedicated to Saint Michael, which became the imperial mausoleum (heroon) of the Komnenos and Palaiologos dynasties. Besides many Byzantine dignitaries, Emperor John II and his wife Eirene, Empress Bertha of Sulzbach (also known as Eirene, and wife of Manuel I Komnenos), and Emperor John V Palaiologos were buried here.
 
During the Latin domination after the Fourth Crusade, the complex was the see of the Venetian clergy, and the icon of the Theotokos Hodegetria was housed here. The monastery was also used as an imperial palace by the last Latin Emperor, Baldwin. After the Palaiologan restoration the monastery was used again by Orthodox monks. The most famous among them was Gennadius II Scholarius, who left the Pantokrator to become the first Patriarch of Constantinople after the Islamic conquest of the city.

Shortly after the Fall of Constantinople the building was converted into a mosque, and the monastery was converted for a while into a Medrese. The Ottomans named it after Molla Zeyrek, a scholar who was teaching there. However, due to its importance in Byzantine history, Zeyrek was one among the few buildings of Istanbul whose ancient denomination was never forgotten. Among others, the church of Pantokrator is remembered by Pierre Gilles in his classic work about Constantinople, written in the sixteenth century. After the completion of the Medreses in the Fatih complex in 1471, the students abandoned Zeyrek,[9] and the rooms of the monastery occupied by the Medrese vanished later.