Istanbul blue mosque. After the Peace of Zsitvatorok and the unfavourable result of the wars with Persia, Sultan Ahmed I decided to build a large mosque in Istanbul to placate Allah. This would be the first imperial mosque in more than forty years. Whereas his predecessors had paid for their mosques with their war booty, Sultan Ahmed I had to withdraw the funds from the treasury, because he had not won any notable victories. This provoked the anger of the ulema, the Muslim legal scholars.

The mosque was to be built on the site of the palace of the Byzantine emperors, facing the Hagia Sophia (at that time the most venerated mosque in Istanbul) and the hippodrome, a site of great symbolic significance. Large parts of the southern side of the mosque rest on the foundations, the vaults and the undercrofts of the Great Palace. Several palaces, already built on the same spot, had to be bought (at considerable price) and pulled down, especially the palace of Sokollu Mehmet Pa?a, and large parts of the Sphendone (curved tribune with U-shaped structure of the hippodrome).

Construction of the mosque started in August 1609 when the sultan himself came to break the first sod. It was his intention that this would become the first mosque of his empire. He appointed his royal architect Sedefhar Mehmet A?a, a pupil and senior assistant of the famous architect Sinan as the architect in charge of the construction. The organization of the work was described in meticulous detail in eight volumes, now in the library of the Topkap? Palace. The opening ceremonies were held in 1617 (although the gate of the mosque records 1616) and the sultan was able to pray in the royal box (hünkâr mahfil). The building was not yet finished in this last year of his reign, as the last accounts were signed by his successor Mustafa I. Known as the Blue Mosque, Sultan Ahmet Mosque is one of the most impressive monuments in the world. It is one of the elements included in the complex built by Ahmed I to compete with Ayasofya.

Hagia Sophia is one of the greatest surviving examples of Byzantine architecture. Of great artistic value was its decorated interior with mosaics and marble pillars and coverings. The temple itself was so richly and artistically decorated that Justinian proclaimed, “Solomon, I have outdone thee!” . Justinian himself had overseen the completion of the greatest cathedral ever built up to that time, and it was to remain the largest cathedral for 1,000 years up until the completion of the cathedral in Seville in Spain.

Justinian's basilica was at once the culminating architectural achievement of late antiquity and the first masterpiece of Byzantine architecture. Its influence, both architecturally and liturgically, was widespread and enduring in the Eastern Orthodox, Roman Catholic, and Muslim worlds alike. The largest columns are of granite, about 19 or 20 metres high and at least 1.5 metres in diameter; the largest weigh well over 70 tons apiece. Under Justinian's orders, eight Corinthian columns were disassembled from Baalbek, Lebanon and shipped to Constantinople for the construction of Hagia Sophia.

The vast interior has a complex structure. The nave is covered by a central dome 55.6 metres (182 ft 5 in) from floor level, supported in part by an arcade of 40 arched windows. Repairs to structure have left the dome somewhat elliptical – with the diameter varying between 31.24 m (102 ft 6 in) and 30.86 m (101 ft 3 in).

The dome is carried on four concave triangular pendentives that serve to transition from the circular base of the dome to its rectangular base.[35] The weight of the dome passes through the pendentives to four massive piers at the corners; these were reinforced with buttresses during Ottoman times, under the guidance of the architect Mimar Sinan.

At the western entrance and eastern liturgical side, the arched openings are extended by half domes carried on smaller semi-domed exedras; a hierarchy of dome-headed elements built up to create a vast oblong interior, crowned by the main dome. Despite all of the aforementioned features, the weight of the dome remained a problem, requiring the addition of external buttresses.

Interior surfaces are sheathed with polychrome marbles, green and white with purple porphyry, and gold mosaics.