Hagia Sophia is the former Greek Orthodox Christian patriarchal cathedral, later an Ottoman imperial mosque and now a museum in Istanbul, Turkey.
It was built in 537 AD at the beginning of the Middle Ages, it was famous in particular for its massive dome. It was the world's largest building and an engineering marvel of its time.
The dome of the Hagia Sophia is supported by the four pendentives of the square corners.
The National Statistics Day (NSD) is celebrated every year in India on 29th June to create public awareness about importance of statistics in socio-economic planning and policy formulation. Note: The 2017 theme is “Administrative Statistics”