"The history of the Albigensian heresy and the holy war waged against them from 1203 to 1218" is a valuable historical source, the author of which is Petrus of Sarnensky. The book describes in detail the events of the struggle against the Albigensians, their beliefs and the causes of the conflict, which led to the bloody events of the Middle Ages. The author offers the reader a deep dive into the atmosphere of that time and an understanding of the complex relationships between religious groups and power structures. This book will help to better understand the historical processes and important events of the Middle Ages in Europe.