Practiced dissecting on animals to get a better understanding of the human body. However he made some errors but these errors were accepted because people of the Church banned questioning his work as they believed his ideas were nearly impossible to improve
Built on the theory of the four humours and focused on the idea of opposites and emphasised the importance of listening to a patient pulse. He also recommended good diet.
Church liked his work because it supported the design theory (God designed humans) Galen called God 'the creator' and the church decided it fitted with their ideas