This book is the Penguin Classics translation of the Res Gestae by Ammianus Marcellinus, the most important primary source for the fourth century in the Roman Empire. As you may notice from the title, it only covers about a quarter of the century, and it spends a lot of time on Julian. Part of the reason is that we are missing the first thirteen books; at some point in the vicissitudes of history, the last copy of them was destroyed or misplaced. However, the book apparently originally started at the end of the first century, so it isn’t clear how much detail there would have been on earlier periods anyway. I gather that the bit historians would most like to still have is Ammianus’s section on Constantine.
So, what about the bit we do have? It’s good classical history. That is, he gives speeches to characters that almost certainly aren’t what they actually said, but which serve to establish character and advance the narrative. It’s also very focused on the doings of emperors, although not exclusively; he also wants to tell us what is happening in Rome, which very few emperors so much as visited in this period. It does, however, focus on Julian. Ammianus was a pagan, and Julian was, in many ways, his hero. Still, he is not entirely uncritical, and is quite harsh about some specific decisions, such as the law banning Christians from basic teaching. He also has an assessment of Julian’s character faults.
This is encouraging; it suggests that his accounts of other incidents may not be too distorted, and they do match quite well with what else we have from the period, allowing for religious bias. He’s a lot more positive about Julian than most of the Church Fathers, for example. There are some lovely incidents, such as the vampire meeting the Goths right at the end, or the exchange between Julian and a prosecutor at a court case. The accused denied the crime (a fraud), and the prosecutor had failed to gather documents to prove his case. Julian acquitted the accused, and the frustrated prosecutor said “Will any be convicted, if a denial is enough to procure acquittal?”. Julian replied “Will any be acquitted, if accusation is enough to secure conviction?”.
There is another incident in which someone informs the emperor that one of his (the accuser’s) enemies is having a purple tunic made. This could be serious; purple was the imperial colour, and making clothes in that colour could indicate plans to bid for imperial power, something that happened a lot in this period. Other emperors tortured people to death for less, but Julian instructed his tailor to send the man a pair of purple boots, to emphasise the emptiness of the symbols without the power.
Governments also seem to have been just as prone to witch hunts against enemies of the state (literal witches, in this case) then as now. It’s a good book, with a good introduction, and, as a primary source on the period, well worth reading if you’re interested in that time. In fact, if you’re seriously interested in the period, it’s essential, and you’ve probably read it already.