Let me state my qualifications for writing historical novels: none. Zero. Nihil.
I have never taken an ancient history course, neither at school nor university. I actually did want to do ancient history at school; I was fascinated by it even then, and also archaeology and palaeontology. Unfortunately my school's timetable had a total clash between the top level mathematics course and ancient history. It had never occurred to them someone might want to do both.
There was never any doubt how that clash was going to get resolved. Maths and science was my future; history was just for fun. Rather ironic I'm now making money from the just for fun bit, but for a few decades beforehand I was earning a fine living from the technical side so it's all come out right.
What I did do was read both Herodotus and Thucydides end to end in my spare time before I was 17. Also Tacitus, Polybius and Plutarch. Since my memory is excellent (he says modestly) I probably could have passed the ancient history exam anyway.
For that matter, I have no writing qualifications either. When I got on the social networking sites, after I'd signed with Janet, people would talk about having an MFA and I had to look up what it meant. English was my worst subject at school.
So if you googled your way here looking for an official, university-approved author with vast qualifications in his subject matter, you've definitely come to the wrong place. This is very much Gary doing it seat of the pants, and having fun as I go.