At the time when the Turks conquered the Byzantium, Constantinople was in the midst of a period of hardship and neglect. As stated by Constantinus and Justinianus, the city was divided into 14 sections. These sections were connected by many roads. The most significant ones were those leading from Beyazit to Aksaray, from there to Cerrahpasa, from Altimermer to Yedikule. Scattered on these roads were numerous squares. The first square which Septimus Severus had built on the hill of Topkapi was adorned by several temples. The Goth Column in the Sarayburnu gate of this square place which Gladius II Goticus (268-270) had erected in memory of the victory he won against the Goths still erects today.

The second one is the Augustaeum square built by Constantinus. This square which Justinianus requested to be done more sumptuously is marble covered with two-storeyed porticos at sides and a monument of the emperor riding a horse takes place at the center. The St. Sophia Church is situated at this place. To the west of the St. Sophia Church there were the Patriarch’s residence, several inns, to the east the Senate building, to the south two palaces and some Turkish baths. The hippodrome was in the southeastern part of this square. This splendid hippodrome which Septimus Severus had commenced and Constantinus had completed was a magnificent building for 30.000 people with a sumptuous Emperor’s Lodge of 500 m length and 118 m width. The hippodrome had a platform called “Spina” in the center of the racing tracks. The Spina was adorned with works of art.

The Four Horses Statue which sits at the entry of the Santa Marco Church in Venice today, once originally stood here. To the east of this platform Constantinus VII Prophyregenetos had the 20.68 m high “Orme Sutun” (Plaited Column) built in 994, however, since the bronze reliefs that once adorned it have been removed by the Latins in 1204, only naked stone can be seen today. Constantinus had the “Burmali Sutun” (Twisted Column) taken from its original place in the Apollo Temple in Delphi and erected it between Dikilitas and “Orme Sutun”. The column consists of the interwound bodies of snakes with three snake heads on top. The most impressive monument of the hippodrome is the “Dikilitas” (Obelisk) that Theodosius I had brought from Egypt in 290 to be erected here. Displaying the victories of Phorao Tutmosis III, this 18 m high obelisk has a marble socket with reliefs of Theodosius and Arcadius. Turks did not give any harm and it was maintained in its original shape until today. Prior to Cemberlitas, there is the Milion Square which is a small square with the basilica on top of Yerebatan Palace opening to it.

The Forum Constantinus in Cemberlitas, the city’s second hill, is surrounded by two-storeyed porticos and in its center is the 57 m high, 9 piece column with the Apollo statue that Constantinus had brought from the Apollo Temple in 328. As Sultan Mustafa II had it encircled by a hoop to prevent its collapse, this column has become known as Cemberlitas (Hooped Stone) up to date.

On the third hill of the city, which is called Beyazit today, there was the Forum Tauri that developed in the period of Great Theodosius and there was a silver statue of Emperor Theodosius I on top of a column. Many roads led to this place in the heart of the city. In Cerrahpasa was a square named after Emperor Arcadius. As the slave market was held here, Turks called it the “Women’s Market”. Being one of Istanbul’s seven hills, it hosted the column erected by Arcadius to symbolize his victory against the Goths in 402. A part of the pedestal of the column is still maintained in “Kadin Sokagi” (Woman’s Street) in Haseki.

The reliefs of Emperor Arcadius and Theodosius are being displayed in the Istanbul Archaeological Museum today. The “Kiztasi” (Maiden’s Stone) Column at the Marcianus Square in Fatih is well preserved to this day. The “Mese Street” that started in front of the St. Sophie Church and ended in Edirnekapi with columns on both sides, and behind them covered colonnade section, where shops took place connected all these squares. The “Great Palace” to the southeast of the St. Sophia Church and Hippodrome that was built during the reign of Constantinus and extended in the Justinianus Period was abandoned in the 13th century and the court moved to Blekarnai Palace.

In the Mosaic Museum at the lower part of the Sultanahmet Mosque, the mosaics of the Great Palace are displayed. The only part of the Blekarnai Palace which was situated between Ayvansaray and Egrikapi that could preserved until today is the Tekfur (Prince) Palace built by Manuel Comnenos I (1143-1180) in the farthest corner in Edirnekapi. When Sultan Mehmet the Conqueror conquered Byzantium, he did not interfere with the religious beliefs of the people and let the churches and monasteries all over the city continue freely with their worship. The Pammakaristos Church built in 1292 was expanded in 1315 when enclosures were built by order of Mikhael Glabas’ wife Maria. This church of which the main cupola is adorned with mosaics portraying Jesus and his 12 apostles was converted into Fethiye Mosque during the reign of Sultan Murat III in 1586. This church in the Carsamba district is open to visit as museum today. The Pantocrator Monastery which Ioannes Comnenos (1118-1143) had built in Zeyrek suffered a looting during the Latin invasion and only the church division of it could preserved. Following the invasion it was converted into the Zeyrek Mosque.

The Chora Monastery in Edirnekapi was built by Emperor Alexi I Comnenos’ mother in-law, Maria Doukania between the years 1077-1081, then restored in the period of Annikos II and expanded due to enclosures made between the years 1315-1321 of which the mosaics were done by Theodoros Metokhites. Today, it serves as Kariye Museum. The St. Nicolas Church in the vicinity of Kariye Monastery was converted into Kefeli Mosque in the Sultan Selim I period and the church which Leon I had built in Ayvansaray in 458 in the name of St. Pierre and St. Maria was converted into Atik Mustafa Pasha Mosque during the reign of Sultan Beyazid II.

The church Justinianus had built in 527 dedicated to St. Serge and St. Bacchus in the Cankurtaran district was converted into St. Sophia the Minor Mosque by Sultan Beyazid II. One of the most impressive buildings of the Byzantium, without doubt, is the St. Sophia Church. Its construction was started during the reign of Constantinus and was opened to worship on 15th February 360. During a revolt against Emperor Arcadius in 404 this church was burned down and was rebuilt by Theodosius II in 415. The new church also was destroyed by a fire that accompanied the Nika revolt in 532 and the present church was built in its place during the Justinianus Period in 537. After the conquest, the St. Sophia Church was converted into a mosque and Sultan Beyazid II and Sultan Murat III had minarets added.

Throughout the course of history it was repaired numerous times and today serves as a museum. The St. Irene Church behind the St. Sophia Church of which the construction dates back to the beginning of the 4th century and completed in the Constantinus period was also destroyed during the Nika revolt in 532, later in the 6th century Justinianus had it rebuilt in its original design. The Fenari Isa (Jesus) Mosque at Vatan Caddesi (street) is the Lips Monastery that was built in the name of Virgin Mary in 907. It was looted during the Latin invasion and turned into a mosque by the order of Beyazid II. The Akateleptos Church in Sehzadebasi that dates back to the IIth century was converted into Kalenderhane Mosque by Sultan Mehmet, the Conqueror and the Hagios Theodorus Church built in Vefa in the 11th century was converted into Vefa Church Mosque by Molla Gurani after the conquest. also the Theodisia Church situated between Unkapani and Ayakapi was converted into Gul Mosque under Selim II and the Hagios Andreas Church in Cerrahpasa belonging to the 7th century was converted into Koca Mustafa Pasha Mosque.

The Imrahor Ilyas Bey Mosque situated between Samatya and Yedikule originally was a monastery, built in 463, but it was converted into a mosque in the Beyazid II period. Besides these religious monuments there are impressive cisterns that the Ottomans inherited from the Byzantium and preserved until today. The remains of the Valance Arch, also called Bozdogan Arch, situated between Edirnekapi and Beyazit was built by Emperor Valance to solve the tap water problem of Constantinople in 368, consists of a 20 m high wall. Opposite the St. Sophia Church the Yerebatan Sarnici (Underground Cistern) that Byzantine Emperor Justinianus had built in the 6th century, measuring 140x70 m. in among the most important works reached to the present day.

It was used for some time by the Ottomans and after being restored it was opened to the public as museum. Situated between Sultanahmet and Beyazit, opposite the Justice Palace takes place the Binbirdirek Cistern which was built by the order of Philoksenos, a Senate member in Constantinus I period in the 4th century. This cistern measuring 66x56 m. was carried by 224 columns consisting of 16 rows each one having 14 columns. Apart from these covered cisterns there were many others like Actius and Aspar that were not covered.

The Kizkulesi (Maiden’s Tower) in Salacak, Uskudar which has become a symbol of Istanbul, was built by the Greek commander Alkibiades in 419 B.C. for the observation of the probable enemies that may come from the Black Sea. The Byzantine Emperor Comnenos converted this tower into a fortress. Kizkulesi, playground of many mythological stories, was rebuilt by the Ottomans and restored as a wooden tower. When this wooden tower burned down, the stone tower that can be seen today was built during the Ahmed III period and its management was assigned to the Lighthouses Office in 1857. The Galata Tower, built by the Genoeses as principal tower of the Galata walls in 1348 is 61 m. high and consists of 12 floors inclusive a cellar. Its roof has been restored and is being used as a restaurant today.

While many of the Byzantine churches have been restored and preserved as mosques, many churches like Hagia Irene, Fethiye and Kariye and primarily the St. Sophia Church today serve as museum for tourists. Besides these splendid Byzantine buildings, the walls of Istanbul has been restored for many times over the years in order to be maintained for the future. For the first time the walls of Constantinus encircling five hills were extended during the Theodosius II period in 412 to cover new districts.

These walls started from the shores of the Marmara Sea extending over a distance of 5 km. up to the Golden Horn shore. Supported by 110 towers, these walls were 15 m. high, and strengthened by a double wall and pits on the land side. The walls of Istanbul have many gates such as Topkapi, Egrikapi and Edirnekapi. Restoration works that started during the Ottoman Empire period have continued ever since in order to carry these treasures for generations to come.