From the back of the book (translated from German):
In the world of Engel, city air makes you free too – at least from the apparently ever-present influence of the Angelitic Church. The Codex Urbanis shines a light on the cities of the Junklords, who have created their own little empires on the rubble of ancient cities, and who resist the Church’s claim to sole power.
Supported by antediluvian finds, forbidden knowledge and treasures found amidst the ruins of the cities, they attempt to stand on their own. The guns and other techonological advances held by their armies and warbands keep even the Engels of the Lord in check.
This book describes countless Diadochs in all their variations from an enlightened doubter to a despot drunk on power, and opens new character options to expand the world of Engel. It deals with the common aspects of life and the circumstances in the church-free cities and offers a glimpse of the forbidden technologies that are at the power of the Junklords.