I took three different boots from their own respective trilogies and made them look like a cohesive trilogy together. Their covers are meant to express the progression that is made within society through the trilogy. The trilogy expands from past to the present to the future. The spine is meant to stick out when placed on a bookshelf, and features the main characters from each of the respective books. 
The back covers are all simply designed reflecting the symbols from each book, and either an important tagline from the book, or an allusion to what the symbols mean. They are accompanied by reviews from respected newspapers and magazines.