This superb dome which seems in its remoteness to belong to the sky rather than the earth, can only be properly viewed from below by taking as reference points the marks cut into the stone; these are fixed in relation to a central mark the extent of the contour. The dome does not form a perfect circle. In the beginning the circumference was exactly regular and the dome somewhat more sharply  in clined, but at its restoration in order to strengthen it further, the present shape was imposed on it. It should not be forgotten that Saint Sophia has stuffed damage from several earthquakes and has been frequently repaired.
   The first great damage occurred in 558. In January 869 after earth tremors lasting 40 days, the dome threatened to cave in . In 986 the dome seemed increasingly on the point of collapse , and the church was closedto the faithful for ten years while expensive repairs were carried out at
a cost of 10.000 Byzantine gold pieces. After this is was reopened for worship; but in 1346, the vault subsided again, and lack of funds precented any repair, so that  the
church remained deserted.

Three Towers of Istanbul

 Galata Tower

THE GALATA TOWER
   The historical origins of the Galata tower are not very clear. Some sources claim that the Roman Emperor Anastasius Dilosus built a lighthouse here in . According to several other sources the tower was built by the Genoese in , after they had settled in the area and erected walls to protect in the new colony. The tower is said to have been rebuilt by Mehmet the Conqueror after the conquest of Istanbul. On the other hand it is known for certain that Sultan Selim II, The conqueror of Egypt had the tower repair in the sixteenth century.

 Historical Tower