Ancient medical treatises had a variety of different ways of classifying and grouping illnesses. Chinese texts like the "Huangdi Neijing" categorized diseases by which of the atmospheric influences was believed to be responsible for them. Many ancient Greek, Mesopotamian, Roman, and Egyptian authors categorized diseases by the body parts they affected, while others divided diseases into acute or chronic illnesses. Mental disorders were classified into categories like mania and paranoia by Hippocrates, and this system was utilized by later authors like Najib ad-Din Samarqandi.