Hagia Irene (Aya İrini) was the first church to be built by the Byzantines, and its history goes back to the 4th century, though its official status wasn't realized until after a fire which occurred in 532. The Eastern Roman Emperor Justinian had the damage caused to the church by the fire repaired in 548. Hagia Irene is also the only Byzantine church to survive to this day with its courtyard still intact. Inside the church you'll find a large cross above gold-gilded mosaics, though its interior would be best described as stark and imposing. Because it was within the walls of Topkapı Palace, the church wasn't converted into a mosque, but it was used as an armory by the Janissaries, the elite infantry units which formed the Ottoman Sultan’s household. It was also used to house an early military museum, and still serves as a museum today. Thanks to its excellent acoustics, it even plays host to selected concerts throughout the year.
In 1898, the timber house standing on a plot of land belonging to Prince Stefan Bogoridi was converted into the St. Stephen Bulgarian Orthodox Church (Sveti Stefan Bulgar Kilisesi). It was consecrated in 1894 with a ceremony in Slavic. After the wooden church was burned down, St. Stephen Church was rebuilt using iron so as not to suffer the same fate again. Its doors opened again in 1898 and was considered not just one of the most elegant buildings on the Golden Horn, but in the whole of Istanbul. Designed by one of the era's leading architects, Hovsep Aznavour, the 500 tons of iron used to build the church were cast in Vienna and shipped over to Istanbul. The church's second consecration was carried out by the Exarch Joseph in September 1898 and was known by Bulgarians as "a pearl in Istanbul's crown". Today, its appearance is no less magnificent and is still a joy to admire.
Hagia Triada Greek Orthodox Church (Aya Triada Rum Ortodoks Kilisesi) is located where Taksim's famous İstiklal Avenue intersects with Sıraselviler Avenue, and it's one of the Beyoğlu district's most recognizable buildings. In contrast to the tendency for Eastern Christian churches to be named after a saint or saints, the name Hagia Triada actually means "Holy Trinity" in Greek. The most significant feature of Hagia Triada which sets it apart from the church which stood there before is its elegant dome, a trademark of Byzantine architecture. The dome is really admirable as it was built after an Ottoman-era ban was lifted that forbid the building of domes in places of worship belonging to minorities. According to inscriptions found in the building's narthex (the part of Byzantine churches which separates the courtyard with walls or columns), Potessaro initiated the construction of the church, Vassilaki Ioannidis had it finished, and it opened to worshipers in 1880. However, some sources suggest the architect Patroklos Kampanaki was in fact the man to complete it. While the church is predominantly Byzantine in style, there are several Neo-Gothic and Neo-classical elements, and even some medieval architectural features too. After exploring Hagia Triada, be sure to spend a little time in its garden, where you can take a break and enjoy its peaceful, calming atmosphere.
After having their original churches converted to mosques and their replacements burn down in various fires, the Dominican monks in Galata learned their lesson and decided to build a sturdier church to call their own. For this, they enlisted the services of Swiss architect Gaspare Fossati, one of the brothers responsible for the restoration of Hagia Sophia. Fossati completed work on the Church of St. Pierre and St. Paul (St. Pierre ve St. Paul Kilisesi) in 1843, and according to the law of the day, the building's façade does not face out onto the street. Built up against the Genoese walls of Galata, the church serves the Italian and Maltese community. In fact, there's a monastery building next to the church which served as an Italian primary school up until 1950. This church has a real medieval feel to it and adds to the esoteric charm of the Galata district.
The Church of St. Anthony of Padua is one of İstiklal Avenue's most striking buildings and has one of the largest congregations in Istanbul. The church's history goes back to the 13th century. After Christian members of the Franciscan order had settled in Istanbul, political upheaval and unfortunate fires meant their area of residence changed several times over the years. At last, in 1724, they located to what is today the Pera neighbourhood in the Beyoğlu district of the city and built a church there. Sadly, in that era buildings, including Catholic Churches, were demolished to make way for a tram system. And so once more they set out to find a plot of land on which to build their new church, and that is where you'll find the Church of St. Anthony of Padua (St. Antuan Kilisesi) today. Building began in 1906, but lack of materials interrupted construction several tımes, and it wasn't finished until 1912. Designed by the architect Giulio Mongeri, Pope John XXIII preached in this church for 10 years, when he was the Vatican's ambassador to Turkey before being elected as pope. As it's the largest church in Istanbul, it's at its busiest during Christian holy days and festivals.
When the Roman emperor Constantine the Great moved the capital of the empire to Istanbul, he brought his interest in (and later conversion to) Christianity with him. He declared tolerance throughout the Empire for the religion, and also called the First Council of Nicaea in modern-day İznik, thereby changing the course of Christianity forever. As the city was the capital of the Roman and later the Byzantine Empires, the Patriarch of the city grew to a position of great importance. Ultimately the Great Schism of 1054 arose and led to a split between the Papacy in Rome and the Fener Greek Patriarchy of the city. When the Ottomans took the city, Fener Greek Patriarchy remained but was placed under the control of the Sultan. However, it still played a role throughout the Ottoman Empire. Since 1586, the patriarchate has been the Patriarchal Basilica of St. George in the Fener district of the city. Though the building is modest from the outside, its importance outweighs its appearance.