Cultural heritage sites are a nonrenewable resource. Today architectural heritage sites are being destroyed at an alarming rate. They're threatened by rising seas, pollution, overtourism, conflicts and so on. Recently, Notre Dame Cathedral has attracted international attention.

Since its main construction from 1163 to 1350, Notre Dame Cathedral repeatedly has been damaged and repaired. On April 15, 2019, the landmark's roof caught fire, causing the collapse of its spire （尖顶） and upper walls severely damaged. Work on the site began quickly. Through the work of photographer Tomas van Houtryve, writer Robert Kunzig, and artist Fernando Baptista, people will see restoring scenes where ruins are cleared and statues saved. Even the COVID- 19 pandemic caused only a two-month delay. Architects have said the expensive project is on track to be completed in 2024.

And    thorny questions arise. What duty do we owe the creations of our ancestors? What lesson can we draw from their presence?

Humankind has answered that differently. In Dresden, Germany, the Frauenkirche, an 18th-century baroque church, was famous for its bell-shaped dome（穹顶） . In February 1945, one of the most destructive bombing attacks of World War II reduced the city to ruins. After German reunion, the church was reconstructed using many of its original stones, as a symbol of peace and harmony. Berlin's Kaiser Wilhelm Memorial Church also fell to bombing but had a different story. Its spire has been left a ruin on purpose to be a "warning monument" against war and destruction.

Like the Frauenkirche, Notre Dame is being rebuilt as close as possible to how it was before, including using the original, toxic metal—lead （铅） —for the roof, causing the debate about how to restore and maintain historic buildings. Actually, no one claims to have the "right" answers on preservation; there may not even be right answers. What people could do is to continuously monitor the global care of cultural heritage sites, as a matter of significance to humanity's past, present, and future.