Hagia Sophia or Ayasofya - A Divine Architectural Achievement

On May 7, 558, in Constantinople, the dome of the Hagia Sophia collapsed. Justinian immediately ordered the dome rebuilt. A short excerpt from the article:

"Third church on exact same spot

The current building was constructed on the site of Byzantium’s acropolis, at the exact same spot where two earlier Hagia Sophias stood. The first was built as a traditional Latin colonnade basilica with galleries and a timber roof, inaugurated on 15 February 360 by Constantius II. It burned down during a riot in 404.

Theodosius II, who inaugurated it on 10 October 405, commissioned the second version. It burned down to the ground during the Nika riots in 532, leaving only several marble blocks which can still be seen in the garden of today’s version.
Only a few days after the destruction of the second Hagia Sophia, Emperor Justinian decided to build the current version, which had to be larger and more majestic than its predecessors.

Dome
Justinian’s cathedral dwarfed all other buildings and was topped by the largest dome ever constructed. A record it held until the arrival of Michelangelo’s dome on top of the St. Peter’s Basilica...

...The original dome collapsed completely during the earthquake of 7 May 558. The emperor ordered an immediate restoration, and lighter materials were used. It was so thin that the hundreds of candles hung high within the Hagia Sophia would cause it to glow at night."