This is the 4868th most frequent Japanese word.
焼失
Destruction by fire.
Here, "焼失" is used to describe the event of the temple perishing in a fire, combined with "しました" to indicate the action took place.
この寺は百年前の火事で焼失しました。
This temple was lost to fire a hundred years ago.
In this sentence, "焼失" indicates the destruction of the archive by fire, and it is associated with "により" to explain the consequence of the event.
資料館の焼失により多くの歴史資料が失われた。
The loss of the archive to fire resulted in the loss of many historical documents.
The word "焼失" here denotes the act of being lost in a fire, and it is part of the expression "焼失を免(まぬか)れた," indicating avoidance of that event.