Simplify the following text for a Grade 10 native English-speaking person.
Original: Many of the old Inca walls were at first thought to have been lost after the earthquake , but the granite retaining walls of the Qoricancha were exposed , as well as those of other ancient structures throughout the city .
Simplified: Many of the old Inca walls were thought to have been lost after the earthquake , but the granite walls of the Koricancha were exposed , as well as many walls throughout the city .