In the seventh century BC, Byzas, the Legendary commander of the Megarians, following the advice of the Oracle at Delphi, founded the city of Byzantium and placed it under the protection of Rhea and Apollon. In 330, the Roman Emperor Constantine decided to transfer the capital of the Empire from Rome to Byzantium. In the new capital, thereafter known as Constantinople, the Emperor initiated the construction of a palace, a forum, the first basilica of Ayasofya and walls encircling the seven hills of the city. When in 476 Rome fell under assaults from the north, Constantinople remained the sole capital of the Empire and gradually moved under Greek political and cultural influence. In the sixth century, with a population of over 400 thousand, it was already a large city.
Attacked by the Avars and the Persians in the 7th and 8th centuries, Constantinople had to defend itself four times against Arab assaults. In 1204 it was occupied by the armies of the fourth crusade which pillaged the city and demolished most of its monuments.

After several attempts over half a century, the Ottomans finally took control of Constantinople in 1453. The Byzantine Empire, now ruling from this city alone, collapsed. When it was conquered by the Turks, Istanbul was a decaying city with a very diminished population. Sultan Mehmet The Conqueror breathed new life into the city and brought in immigrants from the territories of the empire, Moslems and Christians alike.

There are many churches and monasteries active within the city, some of which have been turned into mosques. Studios Monastery Church, Sergios-Bakhos Church, Hagia Eirene Church, Pantakrator Monastery Church, Vefa Church (Hagios Theoderos), Nyrelaion Monastery Church, Eglise D'hagia Thekla Monastery, Eski Imaret Mosque (Pantepoptes Monastery Church), Kalenderhane Mosque (Akataleotos Monastery), Fenari Isa Mosque (Lios Monastery Church) and Fethiye Mosque (Pammakaristos Monastery Church) are the best-known ones.

Saint Sophia (Aya Sofya)
Saint Sophia was, for nearly a thousand years, the largest enclosed space in the world, and still seen as one of the world’s most important architectural monuments. It is one of Turkey’s most popular attractions, drawn by the sheer spectacle of its size, architecture, mosaics and art.

For 916 years it was a church, then a mosque for 481 years, and since 1935 has been a museum. Thought to have been constructed by Emperor Konstantinos I (324 – 337) it was burned down during a revolt. Rebuilt by Emperor Theodosium II, it was opened for worship in 415 and once again was burned to the ground, during the Nika revolts of 532.

Emperor Iustanianus (527 – 565) wanted to construct something even bigger than the original two and appointed architects Isidoros from Miletos, and Anthemios from Tralles to build the Saint Sophia which still stands. Columns, heads, marble and coloured stones were imported to Istanbul from ancient cities in Anatolia for the purpose.

The construction began on 23 December 532, and was completed exactly five years later. The main, central section measured 100m x 70m, covered with a 55m high dome which was a mammoth 30m in diameter – appearing to be a great feat of design. The mosaics are of great importance, and the oldest ones are dominated by geometric and plant motifs decorated with gold.

The worst desecration of the church was in 1204, ransacked by Catholic soldiers during the Fourth Crusade. In 1453, after a failure of the Byzantine Church to fend off the Turks, Mehmet the Conqueror captured the city, rode into Aya Sofia and immediately turned it into a mosque. It was repaired several times, and Islamic ornamentation added, for example an extract of the Koran by calligrapher Izzet Efendi inscribed on the dome. The other reminders of its previous status as a mosque include huge wooden plaques bearing the names of Allah, the Prophet Mohammed and the first four caliphs.

The marble and mosaics remain the most interesting aspects today. The columns supporting the gallery are made from antique marble, and in the western gallery is the green marble which marks the position of the throne of the Empress. The impressive figurative mosaics include Virgin and Child flanked by two emperors, dating back to the late 10th century, and one depicting Christ, the Virgin, and St John the Baptists. Even though there is partial damage, the haunting images on their faces remain as strong as ever. Opening hours: 09.30 - 16.30, daily except Monday.

Hippodrome (Atmeydani)
Back in the rough and ready days of the Byzantium era, elections weren't decided by any kind of namby-pamby voluntary voting system; more often than not an emperor's fate hung on the outcome of a Ben Hur-style chariot race. The races were held at the Hippodrome, or Atmeydani, where the 'Greens' and 'Blues' (political parties) would line up to do battle. Team victories could have an enormous impact on policy and it wasn't unusual for an emperor to lose his throne at the post-match, disappointment-induced riot.

Despite (or maybe because of) its potential to be the site of many a cruel downfall, successive emperors endowed the Hippodrome with many statues, obelisks and monuments. The granite Obelisk of Theodosius is one of the most impressive features. The dainty Kaiser Wilhelm fountain is also worth a visit, as is the Turkish & Islamic Arts Museum (Turk ve Islam Eserleri Muzesi), with its ethnographic exhibits and Ottoman upper-class paraphernalia.

St. Irini (Aya Irini)
This ranks as the first church built in Istanbul. It was commissioned by Constantine in the 4th century, and Justinian later had it restored. The building reputedly stands on the site of a pre-Christian temple.

Kiz Kulesi
Considered to be symbolic of Istanbul, this tiny tower was established on a small island at the entrance of the Bosphorus. In the past, it was used as a watchtower and a lighthouse, until its present purpose of a tourist attraction. Western sources describe this as Leander’s Tower, who was drowned while swimming, to reach his lover Hera. Another story suggests that it was a tower where an emperor’s daughter put her there for security, having dreamt that she would be bitten by a snake.

Galata Tower
The tower was built by the Genoese in 1348, during their occupation of the area, primarily to prevent attacks. Originally known as the Tower of Christ, it stood above the fortification surrounding the Genoese city-state. There is a spiral rock staircase which ascends to the top viewing platform, which today offers visitors spectacular 360 degree panorama of the entire city. The tower was restored in 1967, and an elevator was installed to offer a less tiring alternative to the steep climb. There is also a restaurant on the top floor.

Kariye Museum
This is actually Kariye Mosque, once the 11th century church of St Saviour in Chora, is considered to be the most important Byzantine monument in Istanbul, after Aya Sofia. Whilst unremarkable in its architecture, the interior walls are decorated with superb 14th century mosaics. Illustrating scenes from the life of Christ and the Virgin Mary, these brilliantly colored paintings embody the vigour of Byzantine art. The restored wooden houses in the surrounding area are a good place for relaxation and refreshment.

The church was probably built in the early 12th century, of which only the nave and central apse remain. Theodore Metochites rebuilt it between 1316 and 1321, the same years from which the mosaics and frescoes date, which depict the life of Christ in picture-book fashion. There is a series of mosaics in the form of devotional panels in the narthexes, the theme of which is reflected in the frescoes in the nave and funerary chapel.

Yedikule (Fortress of the Seven Towers)
Any approach to Istanbul will take you past the imposing face of Yedikule. It began life as a triumphal arch in the late 4th century but the arch was then incorporated into the more ambitious plans of Theodosius, who built great land walls around the city and added four towers to the structure. The other three walls were built inside the wall by his successor, Mehmet the Conqueror.

The towers were multifunctional; not only did they help protect the city from attack but were also used as a treasury, a prison and a place of execution. Quite often they were used to accommodate hapless ambassadors from other non-favoured countries. The best view of the city walls and fortress is from the Tower of Sultan Ahmet III, and in some places it's even possible to walk along the land walls.

Yedikule is quite a few miles away from the other city sights and involves a special trip via train from Sirkeci. It's best to go with a group of other travellers as the district often attracts a less-than-salubrious crowd.

Sunken Cistern (Yerebatan Sarnici)
Built in AD 532 and located diagaonally across from Aya Sofya, this is the largest surviving Byzantine cistern in Istanbul. It's builder, Emperor Justinian, incapable of thinking in small terms, built it complete with columns, plinths and a Medusa head or two.

The cistern (sometimes referred to as the Sunken Palace) is 70m (230ft) wide and 140m (460ft) long with 336 columns running down the major corridor. The head of Medusa is carved into two enormous blocks supporting the northwestern corner. Although the cistern has undergone a number of facelifts and a thorough spit, polish and clean between 1985 and 1988, water still drops atmospherically through the ceiling and carp frolic in the water. Coloured lights and Western classical music add a touch of ambience.