The essence of alternate history is to answer the question what if? Consequently an author of such fiction needs to understand the historical context he or she is writing about – at least if one has the desire to write something realistic.
My personal favorite topic of alternate history, and one I might write about, what if Caesarion was not killed? For those who do not know him, Caesarion was the son of Gaius Julius Caesar and Cleopatra VII and according to official records he was killed by soldiers of Octavian (the later emperor Augustus) at age sixteen.
However, Roman historian Plutarch writes that Caesarion was sent to India for his safety but was lured back and subsequently murdered. It is unclear whether he actually made it to India – there was sea traffic between Egypt and India at the time – and he came back or that he was only underway went he returned.
Nevertheless if Caesarion has made it to India then the possibility exist he stayed there safe and well. Then we have to deal with the question who was murdered by Octavian’s soldiers? Probably they killed a look-alike of Caesarion or maybe they just made up the story all together. Neither scenario is without precedents.
Finally we have to answer what Caesarion did in India. Did he have plans to invade the Roman Empire in order to fight and defeat Emperor Augustus? Or did he assimilate with the local population?