Editing Hagia Sophia (section)

===20th-century restoration===
Many mosaics were uncovered in the 1930s by a team from the [[Byzantine Institute of America]] led by [[Thomas Whittemore]]. The team chose to let a number of simple cross images remain covered by plaster but uncovered all major mosaics found.

Because of its long history as both a church and a mosque, a particular challenge arises in the restoration process. Christian [[iconography|iconographic]] mosaics can be uncovered, but often at the expense of important and historic Islamic art. Restorers have attempted to maintain a balance between both Christian and Islamic cultures. In particular, much controversy rests upon whether the [[Islamic calligraphy]] on the dome of the cathedral should be removed, to permit the underlying Pantocrator mosaic of Christ as Master of the World to be exhibited (assuming the mosaic still exists).<ref>{{Cite web |url=http://www.mtholyoke.edu/~allin20b/hagiasophia.html |title=The Hagia Sophia |archive-url=https://web.archive.org/web/20181004092727/http://www.mtholyoke.edu/~allin20b/hagiasophia.html |archive-date=4 October 2018 |website=Mount Holyoke College}}</ref>

The Hagia Sophia has been a victim of natural disasters that have caused deterioration to the buildings structure and walls. The deterioration of the Hagia Sophia's walls can be directly attributed to salt crystallization. The crystallization of salt is due to an intrusion of rainwater that causes the Hagia Sophia's deteriorating inner and outer walls. Diverting excess rainwater is the main solution to the deteriorating walls at the Hagia Sophia.<ref>{{Cite journal |date=1 November 2015 |title=Influence of the Infiltrated Rainwater on the Degradation of the Inner Wall in Hagia Sophia, Istanbul |journal=Energy Procedia |language=en |volume=78 |pages=1353–58 |doi=10.1016/j.egypro.2015.11.153 |issn=1876-6102 |last1=Mizutani |first1=Etsuko |last2=Ogura |first2=Daisuke |last3=Ishizaki |first3=Takeshi |last4=Abuku |first4=Masaru |last5=Sasaki |first5=Juni |doi-access=free|bibcode=2015EnPro..78.1353M |hdl=2433/215879 |hdl-access=free }}</ref>

Built between 532 and 537, a subsurface structure under the Hagia Sophia has been under investigation, using LaCoste-Romberg [[gravimeters]] to determine the depth of the subsurface structure and to discover other hidden cavities beneath the Hagia Sophia. The hidden cavities have also acted as a support system against earthquakes. With these findings using the LaCoste-Romberg gravimeters, it was also discovered that the Hagia Sophia's foundation is built on a slope of natural rock.<ref>{{Cite journal |last1=Friedrich |first1=Jürgen |last2=Gerstenecker |first2=Carl |last3=Gürkan |first3=Onur |date=October 1996 |title=Gravimetric examination of Hagia Sophia's subsurface structure |journal=Journal of Geodesy |language=en |volume=70 |issue=10 |pages=645–51 |doi=10.1007/bf00868226 |issn=0949-7714 |bibcode=1996JGeod..70..645F |s2cid=129375039}}</ref>