I am wondering, is it worth studying math from the original papers as a means to learn a subject? What I am worried about is that some of the methods used to justify results is out dated, or even worse incorrect. As an example, consider Conics. Should I attempt to learn the material by reading the original work as written by Appollonius via translation, or learn it from a modern book that makes refrence to analytic geometry? I have read Euclid's work, and it contains some of the most beautiful mathematics I have ever read... even if the number theory is out dated. To my knowledge, most of Euclid's methods seem rigorous with few exceptions. At the same time, Newtons Principa is said to be out dated and primitive, and learning it would be a waste of time. Is this true of all original work? I am interested in Greek math in particular.