Consisting of The Lion Hunter and The Empty Kingdom, by Elizabeth Wein.
I think I've mentioned this series before, but Wein takes the Arthurian mythos in a direction completely her own. The Winter Prince, the first book, is about Arthur's children in Britain, but A Coalition of Lions, The Sunbird, The Lion Hunter, and The Empty Kingdom are all set in and around Aksum (what is now called Ethiopia). These aren't precisely fantasy in the sense of having (overt) magic, but they are fantastic historical fiction.
The Mark of Solomon, especially The Empty Kingdom, is intense. In fact, I find the size of all Wein's books to be deceptive: there is little that could be called excess, or unnecessary to the story. They are dense and exciting. The Mark of Solomon, which the author refers to as The Adolescence of Telemakos, is rendered in a tight third-person from Telemakos' perspective, although there are a few brief interludes from someone else's point of view, and concerns his coming-of-age. In A Coalition of Lions and The Sunbird, he was shown to be a quiet, canny child, and we see here how he grows to assume adult responsibilities.
I particularly noticed in reading these two books how all three titles can be interpreted in several different ways. In addition, there is almost nothing I can point to and say "That should have been fixed"; my only complaint is that the second book is so intense, it perhaps could have used some comedic relief. You will probably want to have it, and sufficient time in which to read it, at hand before reading the last few pages of the first book.
In short: Great, intense historical fiction. Highly recommended. Refreshingly clean, too, although some heavy issues such as torture are referred to, more so in The Sunbird than here.