To Get Burned
To Be Burned, To Burn, To Get Burnt, To Be Burnt
intransitive verb, ichidan verb
You've seen how 燃やす is to burn something. Now something is just getting burned but you're not doing the actual action yourself. You know this because of the える part which refers to the letter "L" which is getting burned. You like L okay because it stands for "love," but others don't like it so they burn it.
The reading is the same as the word 燃やす.
The castle seemed to be full of the smell of burning wood.