This book is the continuing saga of Ballista, the Warrior of Rome, being the fourth book in the series. I do not recommend reading this book until you read the other three books in the series. All of which are better than this one.
Unlike the other reviews of this book, in my opinion, this is a pretty good book but not as good as the others. I think that is probably because of the story line. In this book, we find Ballista waiting for Gallienus' decision on his fate, because he "assumed the purple" in the last book, albeit for only a few days as a result of killing a usurper to Gallienus. While Ballista is waiting, he experiences an earthquake in Ephesus and the attack of Gothic pirates who he keeps from sacking one city and one town.
Gallienus' decision is to send Ballista to the Caspian Gates, at the edge of the known Roman world, which is the key pass through the Caucasian mountains (between current ex-Russian province of Georgia and Turkey). He is sent there to strengthen the gates from Alani incursions and also to get support from the client kingdoms from the Sassanid King of Kings. At least this is the formal reason. Of course, a main reason for this is to send Ballista into exile where he can't harm the emperor and where he can do some good.
Although the same characters are there: Ballista, Maximus and group and it is of the same period. However, the story doesn't have the same urgency to it. I didn't find myself reading it quickly in order to see what happens next. The story seemed to drag. Again, as I mentioned above, this is probably because of the story line which doesn't have as much imperial intrigue or action as the previous stories.
In spite of that, unlike the other reviews, I do recommend this book, because like the other books in this series, Warrior of Rome, the characters are well developed, and the description of Rome and its environment in the third century are well developed. This author knows the history of Rome and does a good job of translating it to a readable story. If you like Roman history of course, these books will be more enjoyable to you and as I mentioned above, read the previous three books to this series first.