Rosemary Sutcliff community

I was a child under 12 in Southeast Asia when I first read it and I remember that the book was a library copy of the one with the Charles Keeping illustrations, so it must have had everything attached. I remember particularly because it was not too long after I had read "The Lord of the Rings" for the first time, so the "Horse Lord" bit of the title caught my interest at once, even if it wasn't about the Rohirrim! The map and glossary I took as normal for a fantasy novel, which this one might as well have been,, but the geography was definitely secondary to working out what exactly was going on among all these strange, exotic people...