"Battle Studies: Ancient and Modern Battle" is a seminal military history book written by Charles Ardant du Picq, a colonel in the French Army who was killed in 1870 during the Franco-Prussian War. The book is divided into two main parts. In the first part, Ardant du Picq discusses the psychological and emotional aspects of warfare, such as courage, fear, and morale. The second part of the book examines the tactics and organization of ancient armies, with a focus on the Roman legions. Ardant du Picq draws on his extensive knowledge of ancient history to analyze the strengths and weaknesses of different types of units, such as infantry and cavalry, and to offer insights into the tactics and strategies that were most effective in ancient warfare. The final section of the book focuses on modern warfare and the challenges faced by modern armies. Moreover, "Battle Studies: Ancient and Modern Battle" is a highly influential work that offers valuable insights into the nature of warfare and the factors that contribute to success or failure in battle.