Ad Astra: Scipio to Hannibal is the best historical manga I've read, and a great work of historical fiction by any standard. It follows the known history to the letter, while filling in the gaps with compelling interpretations of historical figures and authentic explanations for their actions. It is often the case that creators will insert modern sensibilities or anachronisms into their depictions of ancient times, but the mangaka of Ad Astra avoids these kinds of common pitfalls. Furthermore, he manages to do justice to the wide cast of characters in the Second Punic War, without making any major player seem too perfect or too flawed. Scipio and Hannibal are, of course, well-rounded and brilliant, but it is the secondary major characters such as Fabius and Marcellus who bring the manga to such great heights. Even minor figures like Hadrusbal or Maharbal stand out.
The art is not awe-inspiring, but it more than gets the job done. Hannibal looks like he's being played by Keanu Reeves, but that should not be read as a criticism. In general, characters look distinct without looking cartoonish or unrealistic. Battle scenes are depicted in such a way as to make the overall sequence of events very clear to the reader, while not losing focus on the human element of the conflict. The overall structure of the story is similarly effective at communicating the shifting strategical situation, while taking into account the personal motivations of characters involved. Ad Astra: Scipio to Hannibal does everything right, and almost nothing wrong. Some may enjoy more fantastical or original depictions of history, but if you're looking for a manga adaptation of Polybius, this is the closest thing you'll get. My most substantial criticism is that I wish there was more if it.