Some books just exude such a sense of quality and authority that you know from the moment you open them that they are going to be constantly thumbed and referred to for many years to come. "The Companion to Castles" by Stephen Friar is one of those books, and should be considered essential reading by anyone with the slightest interest in medieval British castles.
The book commences with a brief introduction to the subject, but most of it is given over to an A-Z listing of entries that cover just about every conceivable subject to do with castles. From "Abacus" (The flat slab forming the upper section of a capital) to "Z-Plan" (A distinctive Sottish form of tower house...) the contents are encyclopedic, and what makes this book so valuable is that there are many different types of entry included. Yes, this is the place to look for the meaning of all those obscure terms describing bits of castles, such as a herrison, rainures, or a squinch arch. But the book goes far beyond the narrow definition of the castles themselves in covering aspects of medieval warfare and history, and the wider architecture of the period. Also included are entries which take a much more in depth look at particular topics. Body armour therefore takes up two pages as an entry (with others for specific items of armour such as gorgets, greaves and guiges); while the main entry for "keep" extends to four and a half pages and four illustrations, and runs into "keep-gatehouse", which has two more pages.
It's almost as if the author has set himself the task of explaining every word and expression a reader is likely to encounter in a book of just about any sort about, or involving, a medieval British castle. And as far as we can see, he has succeeded. This is not really a book to read from end to end, but it hugely repays being dipped into or browsed: and, of course, being referred to in response to specific queries.
It is worth noting in passing that this is one of a series of books by the same author and published by History Press. The others are: "The Companion to Local History"; "The Companion to Churches"; "The Companion to Heraldry"; and "The Companion to Cathedrals and Abbeys".