File photos of Notre Dame Cathedral(1/22)

File photo taken on Oct. 11, 2013 shows the interior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Liu Xiao)

File photo taken on Oct. 11, 2013 shows exterior sculptures of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Liu Xiao)

File photo taken on Oct. 11, 2013 shows exterior sculptures of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Liu Xiao)

File photo taken on Oct. 11, 2013 shows the interior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Liu Xiao)

File photo taken on March 23, 2019 shows the exterior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Zhang Cheng)

File photo taken on Oct. 11, 2013 shows the interior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Liu Xiao)

File photo taken on Oct. 11, 2013 shows the interior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Liu Xiao)

File photo taken on Dec. 2, 2016 shows the Notre Dame Cathedral by the River Seine in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Chen Yichen)

In this file photo taken on Feb. 15, 2013, visitors look at a new bronze bell made to celebrate the 850th anniversary of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Gao Jing)

File photo taken in 2000 shows a stained-glass window depicting scenes from the Old Testament at the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Xu Youzhu)

File photo taken on Oct. 11, 2013 shows the interior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Liu Xiao)

File photo taken on June 30, 2017 shows the spire of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Chen Yichen)

In this file photo taken on March 13, 2015, tourists visit the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Chen Xiaowei)

File photo taken on March 23, 2019 shows the exterior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Zhang Cheng)

File photo taken in 1979 shows the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua)

File photo taken on June 30, 2017 shows sculptures on the roof of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Chen Yichen)

File photo taken in May of 1986 shows the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Mu Qing)

File photo taken on March 23, 2019 shows the exterior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Zhang Cheng)

File photo taken on Oct. 11, 2013 shows the interior of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Liu Xiao)

File photo taken on April 7, 2003 shows cherry blossoms near the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Chen Liqun)

File photo taken on June 30, 2017 shows sculptures on the roof of the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Chen Yichen)

File photo taken on June 30, 2017 shows a bell inside the Notre Dame Cathedral in Paris, France. The devastating fire at Notre Dame Cathedral in central Paris has been put out after burning for 15 hours, local media reported on April 16, 2019. In early evening on April 15, a fire broke out in the famed cathedral. Online footage showed thick smoke billowing from the top of the cathedral and huge flames between its two bell towers engulfing the spire and the entire roof which both collapsed later. Notre Dame is considered one of the finest examples of French Gothic architecture which receives about 12 million visitors every year. (Xinhua/Chen Yichen)