The conquest of Istanbul on May 29, 1453, remains one of the most transformative moments in world history, marking not only the rise of the Ottoman Empire as a global power but also the end of the Byzantine Empire after more than 1,100 years of existence.

The city fell following a 53-day siege led by 21-year-old Ottoman Sultan Mehmed II, also known as Fatih Sultan Mehmet, bringing an end to an empire that traced its roots to the Roman Empire.

For centuries, Constantinople, now Istanbul, served as the capital of the Byzantine Empire and a major center of trade and politics. Founded in 330 by Constantine the Great, the city was protected by the Theodosian Walls and remained unconquered for centuries despite repeated sieges.

For centuries, Constantinople, now Istanbul, was the capital of the Byzantine Empire and one of the world's leading political, religious and commercial centers.

Founded by Constantine the Great in 330, the city controlled key trade routes between Europe and Asia. Its Theodosian Walls, built in the fifth century, protected Constantinople from numerous attacks and helped preserve Byzantine rule for more than 1,100 years.

Despite repeated sieges by Persians, Arabs, Bulgars and Rus forces, the city remained unconquered until the Ottoman campaign of 1453.

Istanbul through centuries

The conquest marked not only a military victory but also the beginning of Istanbul's transformation into the Ottoman Empire's capital.

Among the first architectural landmarks erected in Istanbul after the conquest were the Eyüp Sultan Mosque, the Old Palace in Beyazıt, the Fatih Mosque and Complex built by Architect Atik Sinan on the site of the former Patriarchate and Imperial Tomb, the Tiled Pavilion in Gülhane Park, the Rum Mehmet Pasha Mosque in Üsküdar, Topkapı Palace and the cannon foundry in Tophane.

Historical sources indicate that 167 mosques were built in Istanbul following the conquest. These early Ottoman mosques and mescits (small mosques), which helped establish the city’s Turkish-Islamic identity, have largely survived to the present day.

Among the churches and monasteries converted into mosques after the conquest, Hagia Sophia attracted the greatest attention. Originally serving as a church for 916 years, it functioned as a mosque for 482 years and was strengthened during the Ottoman era with additions including minarets designed by the renowned Mimar Sinan, or architect Sinan.

As one of the most enduring symbols of the conquest, Hagia Sophia served as a museum for 86 years following a 1934 decision. It was returned to mosque status by a presidential decree signed by President Recep Tayyip Erdoğan and reopened for worship with Friday prayers on July 24, 2020.

Today, the Hagia Sophia Grand Mosque continues to welcome worshippers as well as local and international visitors, standing as a lasting emblem of the conquest.

Commissioned by Fatih Sultan Mehmet in 1459, the Eyüp Sultan Complex became the first imperial mosque complex established in Istanbul after the conquest.

The complex consisted of the Eyüp Sultan Mausoleum, a mosque, madrassa (religious school), imaret (soup kitchen), sebil (public fountain) and hamam (bathhouse). After suffering severe damage in the 1766 earthquake, the mosque was first repaired and later completely rebuilt before reopening in 1800.

Situated in one of the city's oldest residential areas, the Fatih Mosque and Complex became the first large-scale imperial complex of Ottoman Istanbul.

Built on the orders of Fatih Sultan Mehmet, it sustained damage during earthquakes in 1509, 1557 and 1761 and was reconstructed during the reign of Sultan Mustafa III before reopening for worship in 1771.

The complex included a library, hospital (darüşşifa), cemetery (hazire), clock room (muvakkithane), bathhouse, tomb, soup kitchen, stables and hospice, along with eight major madrassas, eight subsidiary madrassas known as Tetimme, a primary school (mektep) and a Quranic recitation school (darülkurra).

The Mahmut Pasha and Murad Pasha complexes also rank among the most notable architectural projects of the Fatih era.

Construction of the Mahmut Pasha Complex began in 1462 and was completed in 1471. The complex included a mosque, tomb, double bathhouse, inn (han), madrassa, soup kitchen, primary school and court. A fountain and public water dispensary were added later. Today, the mosque, tomb, parts of the inn and bathhouse, and the madrasa classroom remain standing.

Following the conversion of Hagia Sophia, Fatih Sultan Mehmet ordered the restoration of the Pantokrator Monastery in Zeyrek and transformed its rooms into madrassas.

These institutions, regarded as the first educational establishments of the Ottoman Empire in Istanbul, began operating in 1453 and later formed the foundation of Istanbul University.

The first head instructor of the Ayasofya Madrassa was Molla Hüsrev, the teacher of Fatih Sultan Mehmet. The madrassa underwent numerous architectural changes over the centuries before being demolished in 1934.

Another madrassa dating to the reign of Fatih Sultan Mehmet is the Mahmut Pasha Madrassa, located east of the Mahmut Pasha Mosque. Today, only a single classroom from the structure remains.

The city Fatih Sultan Mehmed conquered in 1453 has evolved into a global metropolis of more than 16 million residents and remains the heart of Türkiye's economy, culture and tourism. Straddling Europe and Asia, Istanbul is home to some of the world's most recognizable landmarks and one of the busiest transportation networks in the region.

Beyond its historic landmarks, Istanbul is a global city known for its universities, advanced health care sector, vibrant cultural life and iconic districts stretching from Taksim and Galataport to the Bosporus waterfront.

Yet amid its rapid modernization and status as a global hub, the city's thousands of street cats, cared for by residents and admired by visitors, remain a distinctive symbol of Istanbul's character and heritage.