Celestial Empress' side palace had stood upright for a million years without being destroyed. It was constructed using divine metals and was extremely luxurious, but no matter how luxurious it was, it wasn't able to defend against the collision of a great expert such as Yan'er.
The side palace was in a mess, and over half of the area had been destroyed by the fat bird Yan'er had transformed into. It was especially so when her dragon sparrow primordial spirit had executed her divine art when her primordial spirit came smashing over. As a result, the vermillion bird sacred flames had melted down the side palace, causing molten iron to overflow.
The sacred flame wouldn't stop burning, and so it ignited the other side palaces that hadn't been destroyed.