As a student of history, you've probably already considered the fact that nothing even resembling what we know as 'Penis Enlargement' existed in the pre-modern era . Two reasons why this is very likely: 1) Before just recently (and to this day in many places of the world), people didn't have the sort of disposable time and easy lifestyle that allowed them to spend an hour or more a day lazily stretching and squeezing their penises for a small size increase, and 2) The concept of men feeling insecure and competative about their size is also probably a recent happening. Before pornography was widespread and the other effects of the sexual revolution, men neither knew nor cared much about what the average erection size was, and female pleasure and interest in size was basically a taboo topic. Sure, it was out there, but the idea of penis size being discussed on TV shows and informercials advertising size-increasing pills was pretty far stretch for mainstream society. Basically, concern over female pleasure and the pressure to live up to ridiculous pornographic standards is recent thing that has largely been facilitated by the internet.
For these reasons, you can basically infer that while there might be some mentions of techniques for improving sexual vitality and desire in some ancient texts (which are traditionally far more important components of a healthy sex life, much more so than the recent obsession with penis size), you can be pretty sure that anything you read about jelqing or any other exercise being some sort of ancient regional secret that has been cultivated for millenia is total bullshit. Penis Enlargement as we know it is a recent thing - the stories about ancient roots are made up to lend credibility or they've taken some bit of information out of context.